Add bitly url shortening

Add excludes lists for bitly shortener. Only shorten longer urls.

Make sure config values are set.
Add goodbye plugin
Update readme. Add more information on contributing.

Update git ignore
Fix help command with unknown commands
Reconnect if connection lost
Seen command implemented. Tracks when users are active in the channel.

Goodbye Plugin improvements.
Fix readme

Remove inaccurate comment

Remove long goodbyes, and some of the others
Fix seen reply if bot hasn't seen the user.

Move Users class to seen plugin.

Fix !seen case sensitivity. Update users command doc string