Coloring

* Hacked in support for user defined coloring of the prompt: check it out at `master` now :-)

   - The idea is to use `%f{color_name}` to turn on non-bold foreground coloring, `%F{color_name}` for **bold**/bright foreground text coloring and `%b{color_name}` for background coloring

    - e.g. `prompt "%F%u%F{reset}@%F{black}%h%F{reset}[%F{cyan}%s%F{reset}]::%d%f{green}%g%f{reset}$ %F{resetall}`

* Also added support to show the current git branch with `%g`, if any