Token Parser for Analysis

This PR replaces the regular expressions previously used by the `AnalyzedPHPFile` class with a new `TokenParser` class that takes a files' contents as a string and parses the PHP tokens into a more meaningful format.

Due to the complexity of the TokenParser, I've also added the `AnalyzedPHPFileTest` class which has a number of unit tests for ensuring the proper output of the parser in a number of conditions. More tests will likely be needed, but at least the basics of each feature are tested.

This new token parser has been run against every theme in the public themes repo, all .com themes, and all VIP themes without running into an infinite loop (the regex version would have failed). This does not guarantee the correctness of its' output, but does show that it should not cause the VIP Scanner to become unresponsive.

The new token parser also makes it possible to parse all function calls and variable uses within the code. In the future we can convert checks to using the `AnalyzedFile` class which will significantly speed up the VIP Scanner as each check will no longer have to do string searches or regex searches through the content. Instead, it will just be a search through arrays.

Lastly, I've added doc comment parsing to the token parser, so analyzed functions will come with their doc comments attached - making it easier to understand their purpose.

Closes #97