Added a possibility to display the remote branch and the number of commits you are ahead or behind.

The theme "strug" demonstrates this new funtionality. There are some new variables:

ZSH_THEME_GIT_PROMPT_REMOTE_STATUS_DETAILED : allows you to switch between the current and the new display option.
ZSH_THEME_GIT_PROMPT_REMOTE_STATUS_PREFIX : prefix for the remote status information
ZSH_THEME_GIT_PROMPT_REMOTE_STATUS_SUFFIX : suffix for the remote status information
ZSH_THEME_GIT_PROMPT_AHEAD_REMOTE_COLOR : color for displaying the ahead information (currently only used for the detailed mode)
ZSH_THEME_GIT_PROMPT_BEHIND_REMOTE_COLOR : color for displaying the behind information (currently only used for the detailed mode)