additional DJ features

[chalda]

shout out to @Einarin for the amazing work on the bot! There is now !play which will play a single video (or queue them up if you !play a bunch in a row).

Additional enhancements I am thinking of:

• !playlist - need to check the youtube lib api may be they have this already just need a command for it.
• !playhistory - history of all the youtube plays. Even better, save the bot plays to a youtube playlist or
• !export - save history to a playlist
• some sort of continuous play feature. I am not sure how the youtube api would work for this pro-grammatically but I do love the feature of youtube where it will play videos one after another after your initial play. this would be great for gaming so you dont have to think about music.

[Einarin]

An easy change that would help mitigate #88 would be to persist the playlist to disk so the bot picks up the pieces when it crashes. I don't want to put too much work into it just yet given the the discord.js 0.9 voice apis are still in flux and breaking changes are coming again.