Added formula for bash-git-prompt
Moved bash-git-prompt to correct directory
Updated install and caveats of bash-git-prompt.rb

* install now makes more explicit, what to install
* caveats show now only the path where the gitprompt is installed
Further optimizations on bash-git-prompt.rb

* converted multiple share.install to a single command
* optimized caveats
bash-git-prompt: add 2.0 bottle.