Enable Nodes to provide custom SpiNNaker build functions.
Hookable edge building.
Fixed system memory size change
Adjusted builder registration system
Changed vertex builder to handle __mro__
Added more __mro__ and dummy NengoVertex
Redid __mro__ for edges; PEP8
Merge branch 'master' into plugin_build

Conflicts:
	nengo_spinnaker/builder.py
Merge pull request #21 from ctn-waterloo/plugin_build

Pluggable Builder