rtl_power: clean ^C, cropped bins, +32k bins

Signed-off-by: Steve Markgraf <steve@steve-m.de>
rtl_power: nicer errors, low pass, low bw

Signed-off-by: Steve Markgraf <steve@steve-m.de>
rtl_power: more lowpass options

Signed-off-by: Steve Markgraf <steve@steve-m.de>