This updates all code to make use of the new chainhash package since the
old wire.ShaHash type and related functions have been removed in favor
of the abstracted package.
Also, while here, rename all variables that included sha in their name
to include hash instead.
Since the example illustrates callbacks for the OnBlockConnected and
OnBlockDisconnected callbacks, also register for the notifications with
NotifyBlocks.
While here, document the fact that most of the callbacks require
registration.
