Add GitFlow support

[lbssousa]

I would like to suggest you to provide a GitFlow implementation in your plugin, following this article.

Reference implementation (GitFlow CLI): https://github.com/nvie/gitflow

Just for comparison: Atom's plugin git-control provides a frontend for GitFlow CLI, while Visual Studio Code's plugin vscode-gitflow has its own implementation.

[zaggino]

Thanks @lbssousa , great suggestion. Though it make take some time until I'll be able to implement this.