Support /close to clear current target.
Support /close to clear current target.

Similar to the /close in Pond, /close in xmpp-client will close the
current chat target which may salve your OCD and/or save you from
accidently sending something that you didn't mean to.

This is similar to https://github.com/agl/xmpp-client/pull/75.

paulperegud/xmpp-client,Yawning/ricochet-client,iseeareddoor/xmpp-client,twstrike/xmpp-client,thommfullery/birdcannon,isislovecruft/xmpp-client,agl/xmpp-client