Generic NeuronGroup

[djsaunde]

As in BRIAN, I feel that it would be beneficial to discard objects such as LIFGroup and AdaptiveLIFGroup and replace them with a single, generic NeuronGroup. One would pass in n_neurons (as usual), but also arguments giving the equation(s) of the neuronal dynamics (e.g., 'dv/dt = -v') and other pertinent information (e.g., threshold and reset behavior).

The main hurdle is parsing equations into actionable torch.Tensor operations. (sympy)[http://www.sympy.org/en/index.html] has support for converting symbolic mathematics into theano functions. I'm not sure if we can do something similar, but it would certainly be nice to have. If it were possible, this would be a large and time-consuming addition.