gh flow init command ready

First pull request for `gh git flow` command. 

This will close many tickets that are related to adding `feature` command, while helping users that are not familiar w/ [ Vincent Driessen's branching model](http://nvie.com/posts/a-successful-git-branching-model/). Important to mention that this command is inspired by [nvie/gitflow](https://github.com/nvie/gitflow) and integrated with that tool neatly so users will be able to use the feature built together with `gitflow` until the work is done.

The idea is to allow using the successful git flow methodology but add more feature so you will be able to stream the process better with the pull requests etc.

This initial commit adds the following

1. `gh flow` - get you a help page.
2. Type `gh flow --init` will start the init process to set the directories structure.
3. `gh feature` - help page

`gh flow --init` is appending to the git `config` file, following the same format as `nvie/gitflow` so in case you are using `nvie/gitflow` it will integrate together neatly.