Made git aliasing exit if no git executable is found (which should not
happen, but still) instead of putting all aliases into the conditional.
Added unified colors to git diffs.
Cleaned up formatting of the files.
Fixed git stash alias (gsta) not correctly detecting zsh shell for git
version guessing.
Set default options to automatically rebase on pull, automatically prune
on fetch, and automatically stash and squash on rebasing.
Also made git diff highlight moved code.
