Potentially migrate to discord.py rewrite library

[jellopudding]

discord.py is currently going through a rewrite to make the library conform more to the official API; this may mean that official support for the async branch will go out after the rewrite is complete. I would like to see this bot continue to become more useful and featured.

https://discordpy.readthedocs.io/en/rewrite/migrating.html
https://github.com/Rapptz/discord.py/tree/rewrite