Fix vim config syntax error and use better rspec format for vimux.
Refactor Tmux configuration

- Add OS X-specific pasteboard synchronization
- Use Vim key bindings
- Disable the "mouse mode"
- Shorten the time between Vim sending a command to Tmux and Tmux
  responding back with output.
- Add 5000-ln scrollback history
- Add key bindings for Vi-like movement (h,j,k,l) through panes
- Customize statusbar in the event we are not on an OS X machine running
  iTerm2+tmux