Allow zero sized regions (don't reserve or write to them).
Allow no-decoder ensembles, transmit decoded values after neuron updates.
Merge pull request #36 from ctn-waterloo/no-decoders

Ensembles with no Decoders, Update loop modifications
Merge branch 'refactored-vertices3'

Conflicts:
	nengo_spinnaker/utils/vertices.py
	spinnaker_components/ensemble/ensemble-update.c