Mark ProviderBase.register_provider as private
GTFSRoute should definitely not subclass busbus.Agency
Remove spurious print statement in busbus.util.Lazy
Fix lazy entity properties

It would be nice to have a generic "do this function later" like
busbus.util.Lazy was pretending to be, but that doesn't seem to be
possible in a simple way.

I found code that does what I wanted, albeit not maintained anymore and
using marginally insane metaclasses:
  https://bitbucket.org/rfc1437/lazypy/src/default/lazypy/Promises.py
Fix adding to GTFSMixin._gtfs_id_index
Merge pull request #3 from spaceboats/hello-busbus-fixes

Fixes for "Hello, busbus!"