written a documentation for full module and submodules

This merge closes issue #2 (closed) and its sub-issues : #7 (closed), #8 (closed), #10 (closed) and #37 (closed). It also closes #38 (closed) that was dealt with while writing the documentation.

We have written an external documentation for every submodule and for the main module. The internal documentations were improved with examples and better organisation.

I've also tackled issue #38 (closed) by coding a wrapper function that allowed the filtering function to not be defined in the notebook anymore.