Lock Lita to version 2.3

A private message feature was built into 2.4 which breaks campfire.
Use the room from the event
Provide better error message for RoomNotAvailable
Rename campfire_message double to event
Multi-thread the event receiver

This prevents the http stream from erroring out due to blocking upon
receiving an event. Also prevents long-running responses like meme
generator from blocking trivial responses like karma
Ignore ctags
Upgrade Lita requirement to 2.5
Merge pull request #8 from zacstewart/master

Thread event reception