Two more variables to wrap the git status prompt

$ZSH_THEME_GIT_STATUS_BEFORE and $ZSH_THEME_GIT_STATUS_AFTER can be used to insert text before and after the git status respectively. An example would be to wrap the status with brackets to get something like `foo@~/bar/ (master [+*!])$`. I'm currently working on a theme that takes advantage of this so having this merged back to origin would make my life much easier :-)