Don't kill the preview window

I'm using the preview window for more than just omnicompletion, so I
don't think I want to do this anymore. Tested it for a bit and I think I
like it better this way.
sub: Add new python syntax

One of the contributors to the builtin syntax has his own repo with
recent development. It highlights booleans properly in terms of what
they represent (as boolean values) instead of how they're defined by the
language (as builtins).
Handle bits I don't like in python-syntax

Make shebang comment look normal.
Make imports look like includes.
Add comments for existing setup.