CLI to create new banjo projects

[dabit]

To provide a starting point for every new project, a CLI is needed.

banjo new song_name

Creates the skeleton of a new banjo song. A song.rb file, the channels folder and maybe an example of a channel class.

banjo channel piano

Creates an empty channel class to use on the song.

These are the first few commands that come to mind right now, more can be added as they are needed.