add .gitignore

Contains:
 * common binaries and autogenerated files
 * virtualenv
 * IDE specific files
add sphinx to venv and freeze requirements
set up sphinx documentation generator
move requirements PDF to a new folder
ignore documentation builds
update README.md

Include:
 * instalation instructions for developers
 * links to documentation
remove dependency packages from requirements.txt
remove wsgiref from requirements.txt
Merge pull request #1 from ana-balica/doc-setup

Sphinx documentation tool setup