Added SourceHopperChain subclass of HopperChain.
Not nearly ready to nuggetize yet.

Fish nuggetization is the concept of recognizing a sequence of images
in which the fish hasn't moved at all and processing them all in a lump.
I'm tired of seeing this nearly empty module staring at me accusingly
from the navigation pane of Eclipse.  Judging me.  Taunting me.