Refactor architectural-decision repo into multiple libraries

[cspray]

Right now this repo has the following features:

1. Allow a PHP Attribute to be an Architectural Decision Record through the docblock associated with it.
2. Parse a codebase for the places where a given ADR Attribute is used
3. Generate an XML document detailing all the information about found ADR Attribute and where they're used in the codebase.

Right now, the core feature provided by this library is (1). This feature requires this library to be autoloaded in non-dev contexts. However, features (2) and (3) are not strictly required and introduce external dependencies. Additionally, features (2) and (3) are more of a tool used outside of your application and should be able to be installed in a tools/ directory or in an entirely separate repo and still function correctly.

Features (2) and (3) of this library will be split into its own repo where we can more properly split up responsibilities to reduce the overall number of dependencies required by users implementing this library.