This change reduces memory usage by removing half the number of delay
registers.
This commit also sets up some infrastructure for future work on a fixed
point implementation. Both the floating and fixed point implementations
will run on a 32-bit pipeline for now.
This changes the the lpfCutoffFrequency config variable from a uint32
to a double. This is required because we simplify the sample rate
fraction which cant result in cases where the cutoff frequency is too
aggressively rounded down due to dividing tiny integers.
David Reid