* Resolves
  #40
* Resolves
  #41

As explained in
#40,
this makes it easy to handle to all errors caused by invalid input data
by using `kaitaistruct.KaitaiStructError` in a `try..except` statement.
Three new exception types were added: `InvalidArgumentError`,
`EndOfStreamError` and `NoTerminatorFoundError`. All changes to raised
exceptions in this commit should be backward compatible, as we are only
moving to subclasses of previously raised exceptions.
`NoTerminatorFoundError` is a subclass of `EndOfStreamError` to address
the suggestion in
#41.

Note that the `process_rotate_left` method could only raise
`NotImplementedError` if someone called it manually (because
KSC-generated parsers hardcode `group_size` to `1`, see
https://github.com/kaitai-io/kaitai_struct_compiler/blob/c23ec2ca88d84042edba76f70c1f003d062b7585/shared/src/main/scala/io/kaitai/struct/languages/PythonCompiler.scala#L211),
so it makes no sense to raise an exception derived `KaitaiStructError`
(it's a programmer error, not a user input error). Most of our runtime
libraries in other languages don't even have this `group_size`
parameter, and if they do (C#, Java, Ruby), they also throw the
equivalent of `NotImplementedError` (except the JavaScript runtime,
which throws a plain string, which is _possible_ in JS but considered
bad practice, so we should fix this).