Refactor: Extract code in bin/phpdoc-md into class

[claytonrcarter]

Nothing exciting here! This PR moves all of the code and logic from the bin script into a class, and updates the bin script to instantiate and call that class. Everything appears to be working and the example docs are generated with no changes.

I did add one very minor feature: the .phpdoc-md config file can return an object or an array.

Thanks!

[Kage]

+1

This helps to resolve #8

[Kage]

However, I would recommend making the file operations optional (default enabled). That way you can feed data into and out of the command to test it without actually creating or accessing any files.