GitLab

* Moved git information to left prompt, with
  support for:
    * +ZSH_THEME_GIT_PROMPT_UNTRACKED, MODIFIED,
    STASHED, ADDED, UPSTREAM STATUS
    (if applicable)
* Removed right prompt
* Refactored following Google's guidelines for
  scripts [ http://goo.gl/oJSXH2 ]
    * Using local variables where applicable

Check for at least one commit using a `git log` limit of one.

Improves the performance inside git repos with a large history.

Fixes a bug where color of status arrow in prompt is red even when the exit code was zero (or success). This fix correclty returns green arrow on success and red for non-success exit code.

in the trapd00r theme vcs info is already displayed on the first line if in a version controlled directory. the second vcs info was displayed at the end of the second line without providing additional information. this was removed.

Set the closing square-brace's FG colour to white, to match the opening brace, when the repo directory is dirty.

This avoid spawning additional processes, as the $USER variable will
**always** contain the current logged-in user.

This stops the virtual env name from being printed before it is actually being
used in the zsh prompt.

Fix "command not found: add-zsh-hook" since #3053 removes `autoload -U add-zsh-hook`

Not everyone uses rvm and the library has already got a function for this.

Add spaces before bullet-points to more easily distinguish them from one another and the rest of the prompt when using smaller font-sizes and do not add a blank line prior to prompt output; if there's a desire for spacing, one can use their terminal's line-height to achieve this.

Fixes #2008.

<B> Designates Bisecting
>M< Designates Merging
>R> Designates Rebasing