GitLab

This patch makes git_prompt_status support three new status variables:

 - ZSH_THEME_GIT_PROMPT_AHEAD
 - ZSH_THEME_GIT_PROMPT_BEHIND
 - ZSH_THEME_GIT_PROMPT_DIVERGED

With these extra variables it's easy to see (1) if you have commits in
your local branch that weren't pushed to the remote (AHEAD), (2) if
there are commits in the remote that you haven't merged/rebased yet
(BEHIND) or (3) if you have local unpushed commits AND the remote has
some commits you haven't merged yet (DIVERGED).

Refer to the first line displayed on `git status -b --porcelain`.

An example setup in a .zsh-theme file would be:

ZSH_THEME_GIT_PROMPT_AHEAD="↑"
ZSH_THEME_GIT_PROMPT_BEHIND="↓"
ZSH_THEME_GIT_PROMPT_DIVERGED="↕"

Changes method git_parse_ahead() on git.zsh lib file. Before this
change it checked directly against origin/master branch. Now it
uses $(current_branch) to check for not pushed changes against
the current remote branch.

Modifies the Git lib file (lib/git.zsh), adding three new prompt
methods:

- git_prompt_ahead(): Shows the content of the custom var
  $ZSH_THEME_GIT_PROMPT_AHEAD if the local repository has
  commits ahead from the remote origin repository

- git_prompt_short_sha(): Shows last commit SHA hash in short
  mode wrapped between the content of the custom vars
  $ZSH_THEME_GIT_PROMPT_SHA_BEFORE and
  $ZSH_THEME_GIT_PROMPT_SHA_AFTER

- git_prompt_long_sha(): Shows last commit SHA hash in long
  mode wrapped between the content of the custom vars
  $ZSH_THEME_GIT_PROMPT_SHA_BEFORE and
  $ZSH_THEME_GIT_PROMPT_SHA_AFTER

Initial implementation of a new plugin system, so that people can managed which aliases/functions they want.

(via git status -s, benchmarked)

Moving all zsh config options into a lib/ subdirectory to make way for some upcoming changes to directory structure and configuration options

`git-symbolic-ref` needs to be `git symbolic-ref`

 * Improved speed, the first time cd'ing into a git repo the prompt
   returns much faster (for me at least).
 * Prompt is now decorated in nested folders within a git repo. No
   longer check for the '.git' folder.

 * 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.