Use set to accelerate netlist building
Use set to accelerate netlist building

When querying which connections are sourced at which filters using a set
to store the data is considerably faster than using a list
(not surprisingly...). This results in a 14s speed-up on the build time
for a 256-D circular convolution network on my laptop.

project-rig/nengo_spinnaker,project-rig/nengo_spinnaker,project-rig/nengo_spinnaker