GitLab

Based on Evan's prompt, it uses colors, shows the exit status of the
last command if it was non-zero, and displays "#" when running
with elevated privileges

 * git.zsh is now themable:
   * git_prompt_info() now will look in the following variables for
     formatting strings:
     * ZSH_THEME_GIT_PROMPT_PREFIX - Prefix for the prompt (before the
       branch name)
     * ZSH_THEME_GIT_PROMPT_SUFFIX - The very end of the prompt
     * ZSH_THEME_GIT_PROMPT_DIRTY - Displayed when the branch is dirty
     * ZSH_THEME_GIT_PROMPT_CLEAN - Displayed when the branch is clean
 * Updated geoffgarside, robbyrussell, and maran to work with new git
   theme
 * Added the Risto theme, which is very similar to a number of bash
   prompts, and allows me to use zsh in with out my co-workers knowing I
   have the advantage. Think of it as a ninja theme.

Adding theme support so that people can share their zsh prompts with others. Users can set which theme to load in zshrc now.