* (experiment) measure effect of IF gain on baseband SNR
* (experiment) measure effect of IF gain linearity on baseband SNR
* (experiment) measure effect of RTL AGC mode on baseband SNR
* (experiment) measure effect of ADC calibration on baseband SNR
* (experiment) measure effect of IF bandwidth on baseband SNR
* (experiment) measure effect of IF sample rate on baseband SNR
* (experiment) try if RTL AGC mode improves FM decoding

* (feature) support 'M' 'k' suffixes for sample rates and tuning frequency
* (feature) implement off-line FM decoder in Python for experimentation
* (feature) implement stereo pilot pulse-per-second
* (quality) consider DC offset calibration
* (speedup) maybe replace high-order FIR downsampling filter with 2nd order butterworth followed by lower order FIR filter
* figure out why we sometimes lose stereo lock
* it looks like IF level sometimes varies so much that it saturates the receiver; perhaps this can be solved by dynamically managing the hardware gain in response to level measurements
* (quality) figure out if I/Q balance can improve weak stations
* (quality) figure out if hardware gain settings can improve weak stations
* (feature) implement RDS decoding
* (quality) consider FM demodulation with PLL instead of phase discriminator