Add /shrug command
Certain popular web-based chat systems support a `/shrug` command which
appends the ¯\\_(ツ)_/¯ text emoticon (kaomoji) to a message. I've often
found myself wishing Riot had something similar, so I decided to add it
myself. (If Riot ever gets a user-extensible /-command system, this will
probably no longer be necessary. But since it doesn't have that, here I
am). Doesn't support markdown / rich text messages because I didn't want
to dig that far into Riot/the SDKs for my first PR; if someone else
would like to add that, by all means.
Signed-off-by: Andrew Chronister <chr@chronal.net>
