Switch to sourcify for better character counting

This allows to only count the method body and ignore the method
definition which better reflects the algorithm used.
Refactor minitest plugin into distinct files
Make alle whitespace not count, not just spaces
Also count called methods within RubyGolf
Don't infinitely count recursive method calls
Also count method calls using class or self

* RubyGolf.doit
* RubyGolf::doit
* rg = RubyGolf; rg.doit