Add more unit tests

[herzbube]

Notes about the current test coverage.

[DONE] = tests exist
[OK] = no tests exist, but there's an explanation why that's ok for the moment

- src
  - [DONE] document
    - [DONE] typedproperty
      - [OK] SgfcBoardSizeProperty.h
        >>> Logic already tested via SgfcPropertyDecoder. Might be worth adding tests later.
      - [OK] SgfcGameTypeProperty.h
        >>> Logic already tested via SgfcPropertyDecoder. Might be worth adding tests later.
    - [DONE] typedpropertyvalue
      - [DONE] go
        - [OK] SgfcGoMovePropertyValue.h
          >>> Logic already tested via SgfcPropertyDecoder. Might be worth adding tests later.
        - [OK] SgfcGoPointPropertyValue.h
          >>> Logic already tested via SgfcPropertyDecoder. Might be worth adding tests later.
        - [OK] SgfcGoStonePropertyValue.h
          >>> Logic already tested via SgfcPropertyDecoder. Might be worth adding tests later.
      - [OK] SgfcColorPropertyValue.h
        >>> Logic already tested via SgfcPropertyDecoder. Might be worth adding tests later.
      - [OK] SgfcDoublePropertyValue.h
        >>> Logic already tested via SgfcPropertyDecoder. Might be worth adding tests later.
      - [OK] SgfcMovePropertyValue.h
        >>> Logic already tested via SgfcPropertyDecoder. Might be worth adding tests later.
      - [OK] SgfcNumberPropertyValue.h
        >>> Logic already tested via SgfcPropertyDecoder. Might be worth adding tests later.
      - [OK] SgfcPointPropertyValue.h
        >>> Logic already tested via SgfcPropertyDecoder. Might be worth adding tests later.
      - [OK] SgfcRealPropertyValue.h
        >>> Logic already tested via SgfcPropertyDecoder. Might be worth adding tests later.
      - [OK] SgfcSimpleTextPropertyValue.h
        >>> Logic already tested via SgfcPropertyDecoder. Might be worth adding tests later.
      - [OK] SgfcStonePropertyValue.h
        >>> Logic already tested via SgfcPropertyDecoder. Might be worth adding tests later.
      - [OK] SgfcTextPropertyValue.h
        >>> Logic already tested via SgfcPropertyDecoder. Might be worth adding tests later.
      - [OK] SgfcUnknownPropertyValue.h
        >>> Logic already tested via SgfcPropertyDecoder. Might be worth adding tests later.          
    - [OK] SgfcComposedPropertyValue.h
      >>> Logic already tested via SgfcPropertyDecoder. Might be worth adding tests later.          
    - [DONE] SgfcDocument.h
    - [DONE] SgfcGame.h
    - [DONE] SgfcNode.h
    - [OK] SgfcProperty.h
      >>> Logic already tested via SgfcPropertyDecoder. Might be worth adding tests later.          
    - [OK] SgfcPropertyMetaInfo.h
      >>> Hardly worth testing because it's used only internally and the logic consists of one giant switch-statement, or is based on the value type descriptors.
    - [OK] SgfcSinglePropertyValue.h
      >>> Logic already tested via SgfcPropertyDecoder. Might be worth adding tests later.          
    - [DONE] SgfcTreeBuilder.h
        
  - factory
  - [DONE] game
    - [DONE] go
      - [DONE] SgfcGoMove.h
      - [DONE] SgfcGoPoint.h
      - [DONE] SgfcGoStone.h
    - [OK] SgfcBoardSize.cpp
      >>> Relatively simple data container, with a bit of logic. Might be worth adding tests later.
  - interface
    - internal
    - public
  - parsing
    - [DONE] propertyvaluetypedescriptor
      - [OK] SgfcPropertyBasicValueTypeDescriptor.h
        >>> Relatively simple data container, with almost no logic. Hardly worth testing because it's used only internally and only with hardcoded data.
      - [OK] SgfcPropertyComposedValueTypeDescriptor.h
        >>> Relatively simple data container, with almost no logic. Hardly worth testing because it's used only internally and only with hardcoded data.
      - [OK] SgfcPropertyDualValueTypeDescriptor.h
        >>> Relatively simple data container, with almost no logic. Hardly worth testing because it's used only internally and only with hardcoded data.
      - [OK] SgfcPropertyElistValueTypeDescriptor.h
        >>> Relatively simple data container, with almost no logic. Hardly worth testing because it's used only internally and only with hardcoded data.
      - [OK] SgfcPropertyListValueTypeDescriptor.h
        >>> Relatively simple data container, with almost no logic. Hardly worth testing because it's used only internally and only with hardcoded data.
    - SgfcDocumentEncoder.h
      >>> This needs testing. It's not yet clear how exactly, though. Indentation makes things harder to test than necessary, also platform-specific line endings (std::endl) might become an issue.
    - [DONE] SgfcPropertyDecoder.h
    - [DONE] SgfcValueConverter.h
    
  - [DONE] sgfc
    - [DONE] backend
      - [DONE] SgfcBackendController.h
      - [OK] SgfcBackendDataState.h
        >>> only an enum type
      - [DONE] SgfcBackendDataWrapper.h
      - [OK] SgfcBackendLoadResult.h
        >>> Simple data container
      - [OK] SgfcBackendSaveResult.h
        >>> Simple data container
      - [OK] SgfcOptions.h
        >>> There's not much that can be tested here. The only imaginable test
            would be to check whether a capture/restore cycle restores the correct
            values.
    - [DONE] frontend
      - [DONE] SgfcCommandLine.h
      - [OK] SgfcDocumentReadResult.h
        >>> Relatively simple data container, with a bit of logic. Might be worth adding tests later.
      - [DONE] SgfcDocumentReader.h
      - [OK] SgfcDocumentWriteResult.h
        >>> Relatively simple data container, with a bit of logic. Might be worth adding tests later.
      - [DONE] SgfcDocumentWriter.h
    - [DONE] message
      - [DONE] SgfcMessage.h
      - [DONE] SgfcMessageParser.h
      - [DONE] SgfcMessageStream.h
    - [DONE] save
      - [DONE] SgfcSaveStream.h
      - [DONE] SgfcSgfContent.h
  - [OK] SgfcPrivateConstants.h
    >>> There's no need to test a passive constants container class.
  - SgfcUtility.h
  
- include
  - [OK] ISgfcBoardSizeProperty.h
  - [OK] ISgfcColorPropertyValue.h
  - [DONE] ISgfcCommandLine.h
  - [OK] ISgfcComposedPropertyValue.h
  - [DONE] ISgfcDocument.h
  - [OK] ISgfcDocumentReadResult.h
  - [DONE] ISgfcDocumentReader.h
  - [OK] ISgfcDocumentWriteResult.h
  - [DONE] ISgfcDocumentWriter.h
  - [OK] ISgfcDoublePropertyValue.h
  - [DONE] ISgfcGame.h
  - [OK] ISgfcGameTypeProperty.h
  - [DONE] ISgfcGoMove.h
  - [OK] ISgfcGoMovePropertyValue.h
  - [DONE] ISgfcGoPoint.h
  - [OK] ISgfcGoPointPropertyValue.h
  - [DONE] ISgfcGoStone.h
  - [OK] ISgfcGoStonePropertyValue.h
  - [DONE] ISgfcMessage.h
  - [OK] ISgfcMovePropertyValue.h
  - [DONE] ISgfcNode.h
  - [OK] ISgfcNumberPropertyValue.h
  - [OK] ISgfcPointPropertyValue.h
  - [OK] ISgfcProperty.h
  - ISgfcPropertyFactory.h
  - ISgfcPropertyValue.h
  - ISgfcPropertyValueFactory.h
  - [OK] ISgfcRealPropertyValue.h
  - [DONE] ISgfcSgfContent.h
  - [OK] ISgfcSimpleTextPropertyValue.h
  - [OK] ISgfcSinglePropertyValue.h
  - [OK] ISgfcStonePropertyValue.h
  - [OK] ISgfcTextPropertyValue.h
  - [DONE] ISgfcTreeBuilder.h
  - [OK] SgfcBoardSize.h
    >>> Relatively simple data container, with a bit of logic. Might be worth adding tests later.
  - [DONE] SgfcColor.h
  - [DONE] SgfcConstants.h
  - [DONE] SgfcCoordinateSystem.h
  - [DONE] SgfcDouble.h
  - [DONE] SgfcExitCode.h
  - [DONE] SgfcGameType.h
  - [DONE] SgfcGoPointNotation.h
  - [DONE] SgfcMessageType.h
  - SgfcPlusPlusFactory.h
  - [DONE] SgfcPropertyType.h
  - [DONE] SgfcPropertyValueType.h
  - [DONE] SgfcTypedefs.h
- sgfc
  - ?

[herzbube]

Document tags. Example: [filesystem] = all tests that interact with the filesystem.

To exclude a tag: ./test/libsgfc++-test "~[filesystem]"

[herzbube]

Make a test that makes use of every public type, to verify that all types are exported on Windows.

[herzbube]

Loading and saving SGF content have been implemented. Add tests for

• SgfcCommandLine::LoadSgfContent
• SgfcCommandLine::SaveSgfContent
• SgfcDocumentReader::ReadSgfContent
• SgfcDocumentWriter::WriteSgfContent