Download release tarballs instead of cloning the repos.

The repos were just getting too big. the zips are much smaller.

Conflicts:
	install.sh
install: Convert the zip vim plugin installer to Python.
install: Add logic to download vim plugins and install.
install: Simplify the zipfile download.
install: Account for the top-level dir in the zips.
install: Fix the pathnames. Top-dir comes first.
install: Properly remove the temporary file.
install: Remove last little nuisance.
Merge branch 'python3_unzip'

Port functionality of downloading zip files and extracting a certain
portion into the .vim folder structure.