BF: This is required in order to import everything properly.

Why are there two different pyx modules `MakeFastRF` and `MakeFastRFs`? ATM, they seem to contain the identical content. Is there a future plan for these to diverge? At any rate, they are both required in order to import `simulation` cleanly, because they are both being imported here:  https://github.com/arokem/popeye/blob/master/popeye/simulation.py#L5