Use hard tabs in .gitconfig

Using git config to manage this file results in hard tabs. This commit
replaces all of the soft tabs with hard ones to help improve future
consistency, and adds the Vim configuration that will use hard tabs in
this file in the future.
Slate: update references to iTerm -> iTerm2
Vim: tweak snippets

I've collected a few snippet tweaks over the past couple of months that
need to be committed.
Vim: add some more of my common typos to abbreviations list
Vim: add "inline" to dictionary