Turns out 0x10088000 - 0x10089fff is not the right place. It's 0x40041000, and is only 256 bytes!
Move PPM to correct place, change representation to PPB for finer control.
Reset PPB value to initial value if read value out of bounds.
Clip PPB value on write to permitted bounds.
Contributes to resolution of issue #11.
Move channel filter frequency determination to baseband side, where the filtering is determined and performed.
Add useful accessor methods to BlockDecimator.
Channel spectrum decimation now accounted for when computing filter frequencies.
Renamed a bunch of variables relating to channel spectrum bandwidth and filter frequencies.
