Created the lingon cli & added a help flag: lingon -h

* The lingon command can now be installed globally with npm install -g lingon.
* `lingon -h` provides help and a list of supported arguments.
* Also added the ability for plugins to to provide help messages for the tasks they define.

Change-Id: I9fb3e9f8eeca37ae6f8ee8047dab56995754b25b