Adds `vim-ruby` back to `vimrc.bundles`

Removal in https://github.com/thoughtbot/dotfiles/commit/deb7ee5948a0df56c2a68fc2dab22fd31d70a204
was accidental.

Also, removes `vim/bundle` directory as it is no longer useful to us, since
`vundle` creates it when it needs to.
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.
Ignore vim/spell in Git

* Also sort gitignore's list items.
* Also ignore vim/.netrwhist.
* Set spellfile to Dropbox-based location.