Add documentation.

Add auto-generated documentation. Note that 95.96 % is undocumented.

Suggestion on documenting each module in lib or other *.rb
# here we say what does this *.rb does
# task:
# Author: author_name
# Date: data
# Copyright: copyright

I'll manage to develop a website for both betty and its documentation in either in jekyll(this way we can run it on Github server) or in Sinatra(this way i push it on betty.herokuapp.com). What do you think?