Allow stylesheets to autocomplete hyphenated words
Add /usr/local/bin to PATH before /usr/bin

This is for homebrew binaries to work.

Load `rbenv` after adding `$HOME/.bin` and `/usr/local/bin` to `PATH`, but
before adding project-specific binstubs.
tat command now works in directories with periods

- Running `tat` in the robots.thoughtbot.com directory was throwing a
'bad session name' tmux error
- See http://sourceforge.net/p/tmux/tickets/109/
Set Vim's spellfile to $HOME

Running `zg` adds words to the `spellfile`:

https://github.com/thoughtbot/dotfiles/commit/4f5a2edc336970b8a1c7eded3934182810abeb20
http://robots.thoughtbot.com/vim-spell-checking

Setting the spellfile keeps it out of its default location, `vim/spell`, which
would otherwise be inside thoughtbot/dotfiles. We don't necessarily want to
share the `spellfile` across the team.
Make it easy to checkout GitHub pull requests

This alias makes the following workflow possible:

Look at changes:

    git co-pr 123
    git diff origin/master

Bundle, validate tests are passing:

    bundle
    rake

Rebase interactively, squash, and potentially improve commit messages:

    git rebase -i master

Merge code into master:

    git checkout master
    git merge pr/123 --ff-only

Push:

    git push origin master

Clean up:

    git branch -D pr/123