Have a method of dumping other user's information

[khyperia]

Possible features:

1. Dump username, nickname, game status, discord ID, all mutual servers, etc. of any user specified
2. List people in channel, their roles, etc.
3. List people in server, server roles, channels in that server, emojis, possibly voice channels, who is in what voice channel, etc.
4. Things and stuff that are in the discord::State object that I forgot about when writing this issue.

Possible design:

/discord info [anyID|username|nickname|channelname|servername|etc]
/whois [thing] - would probably be really bad, as weechat doesn't support overloading of commands to be different plugins based on different buffers (would have to do shenanigans with the irc plugin's /whois command)
/info [thing] - or some other unique global command
/discord info channel [channel] - /discord info server [server] - etc.