Ack: Add .sass-cache to ack ignored directories

This directory only contains compiled stuff that I don't care about
searching through.
Vim: remove vim-expand-region mappings

I recently removed this plugin and forgot to remove my mappings for it.
Vim: map <esc> to clear search highlighting

I've grown accustomed to typing something like `/arst` to clear search
highlighting in vim. With this mapping, I can just press `<esc>`
instead.