Kill Oh My ZSH

* Add pure prompt (https://github.com/sindresorhus/pure)
* Add tomorrow theme to iTerm and vim (https://github.com/chriskempson/tomorrow-theme)
* Import some aliases from Oh My ZSH (directory and git-related stuff)
* Add zsh-syntax-highlighting https://github.com/zsh-users/zsh-syntax-highlighting
* Removed `prq` function. Use `gh` instead.
* Vim: Remove spelling settings as it was highlighting words all the time
Tmux confs