Add 'get_pymodule' method to 'project'.

This hides some of the 'pycore' functionality and provides a much more
descriptive name.
Update documentation because rope's using GitHub now.
Move get_python_files from pycore into project.

All access of get_python_files are an indirection from project. And the
method itself calls a method that's within the project object. Moving
the method into project cleans this up.
fix naked drive colon paths on win32 cygwin python
fixed buggy cygwin special casing
remove unneccessary temp rv variable