Fixed some spelling errors in the README file
Enhanced comments, Restructured file

Moved some functions around so that they are better structured in the
file. Additionally added some more docstrings as well as other
documentation.
Added stop directory to find_recursive method, Cleaned up imports

Removed some unnecessary imports from the file.

Added a stop directory to the find_recursive method which allows early
exit from the method if one does not want to check until the root
directory.
Added more valid source extensions for C and CPP
Added a method which adds flags to a list in a save manner

This method adds flags without creating conflicts with already existing
flags as well as without creating duplications of already exiting flags.

Therefore it needs a special format of the additional flags which is
documented in the method.
Enhanced documentation