install: Start conversion to Python.
install: Break symlinks and min_files into functions.
install: Ensure certain folders exist at the start.
install: Add git configs.

Also, try converting to Python3. It's about time we start using it.
bash: Use git prompt for bash_completion package.
install: Use Python3's input instead of raw_input.
install: Set git config if non-existent.
install: Refactor the code a bit.
Merge branch 'convert_installer_to_python'

This branch converts the installer to Python 3. For the moment I still
have the bash version as well.

The Python installer is still missing a few features:
- Checking for installed programs.
- Installing rvm.
- Setting up the eatmydata links.