Gcspypi

- migrated parsing logic to parsers/*
- added verbose mode
- added interaction flag to remove command
- added logic to handle repository specified in ~/.gcspypirc
- added gitlab-ci integration
- achieved 100% coverage (parsing code ignored, but there's no logic there)

- fully replaced unittest with pytest
- added pytest-runner, to invoke tests like : `python setup.py test`
- fixed relative imports, tested on python3 and python2.

- Added support for Python 3.6
- Added support for installing requirements.txt
- Fixed version ordering

Added ability to control whether packages are installed in user home or not (via `pip install ... --user`)