f222ce9969
Main goal: a lot of nested future/result folding. This mainly modifies error handling for Tracks and TrackHandles to be more consistent, and hides the underlying channel result passing in get_info. Errors returned should be far clearer, and are domain specific rather than falling back to a very opaque use of the underlying channel error. It should be clearer to users why their handle commands failed, or why they can't make a ytdl track loop or similar. Also fixed/cleaned up Songbird::join(_gateway) to return in a single await, sparing the user from the underlying channel details and repeated Errs. I was trying for some time to extend the same graces to `Call`, but could not figure out a sane way to get a 'static version of the first future in the chain (i.e., the gateway send) so that the whole thing could happen after dropping the lock around the Call. I really wanted to fix this to happen as a single folded await too, but I think this might need some crazy hack or redesign.
Songbird examples
These examples show more advanced use of Songbird, or how to include Songbird in bots built on other libraries, such as twilight or serenity.