Remove all the messages for a fingerprint when muted.

I think this is a better behavior for things you don't want to see
(e.g. penises). In the future we should probably add some sort of undo
function for the last mute (accidental mutes seem to happen a lot), in
which case we might need to rethink the removal (keep the muted chats
somewhere so we can bring them back, perhaps?).
Remove as many chats as necessary to get under the limit.

Before, if you scrolled up in an active meatspace, you could end up
with a large number of chats in your buffer. When a new chat came in,
only the top one would be removed, leaving you with an equilibrium
potentially much higher than the actual limit.

With this change, when a chat comes in and a user is scrolled to the
bottom, all of the chats above CHAT_LIMIT will be removed, instead of
just the top one.
Update to latest Animated_GIF and explicitly free workers. Fixes #103
Merge pull request #167 from tec27/mute_removal

Remove all the messages for a fingerprint when muted.
Merge pull request #168 from tec27/chat_limits

Remove as many chats as necessary to get under the limit.