Permit non github urls

Antigen is so good it shouldn't be restricted.

Don't really know a good way to handle the user@host type thing apart
from just looking for an @.
Remove .env and a better Makefile.
It appears git changed its outputs a little bit.

The line `Checking connectivity... done` has been added to git's output. We need
to find a more reliable way to test these that doesn't break with git's output
changes.
Added a note referencing #78 in the readme.

There is a comment giving background on the theme command.
Merge upstream.
Merge PR for allowing other urls. Fix #77.