renamed RingBuffer.next to RingBuffer.prev because it goes backwards through the buffer, which could be confusing.
added parameters to set a minimum word length and compare case insensitive.
now cycles through the completions lexically sorted.
Auto-complete names of users not connected anymore b/c there's a good chance they might be back at some point & you want to address them while they're gone.
added a check to Completor.add to ignore empty or duplicate entries
fixed a minor, completely inconsequential inconsistency in the use of this/self :|