Add invite management functions.
Add invite management functions.

mgardne8/discord.py,Harmon758/discord.py,lgkern/PriestPy,variablehair/Eggplantato,khazhyk/discord.py,Harmon758/discord.py,Rapptz/discord.py,jhgg/discord.py,Theoretical/UselessBot,imayhaveborkedit/discord.py,rapptz/discord.py