Unread count on the Favicon

Add the count of unread messages to the favicon.

Why would you want the count on the favicon?

You may be wondering why this is a thing (in addition to unread messages on the title)... and the reason is that I pin tabs. When I do, I like to know what's going on. But I couldn't pin the Slack tab because I wouldn't know if I had unread messages (their icon doesn't really show a state other than "there are unread messages somewhere" or "you were mentioned").

When this plugin is enabled, the favicon shows the number of unread messages on the channel you have selected.

How does it look?

Here's a gif... keep an eye on the pinned tab. I don't looove how it looks, so if you know how to play with canvas and make it nice, I'd love your help! here you can see how I'm building it.