Support LIF.min_voltage

[tcstewar]

At the moment, nengo_ocl doesn't support LIF.min_voltage values other than 0. How hard would it be to add support for this? Would it just be a matter of adding it to https://github.com/nengo/nengo-ocl/blob/nengo-dev/nengo_ocl/simulator.py#L872 and adjusting https://github.com/nengo/nengo-ocl/blob/nengo-dev/nengo_ocl/clra_nonlinearities.py#L958 and https://github.com/nengo/nengo-ocl/blob/nengo-dev/nengo_ocl/clra_nonlinearities.py#L977 ?

[hunse]

You'd have to make it a parameter like tau, ref and amp, and pass it in that way. So that would change some of the function you identified in simulator.py, and more of the one in clra_nonlinearities.py. But overall, not too difficult.