added some minor options

[hayguen]

added option -L to print current level values added option -c to configure de-emphasis time constant for wbfm added option -v to print verbose (debug) output added alias modulation names nbfm, nfm, wfm

[hayguen]

• option -L: "rtl_fm -L 10 -M fm": prints current level to stderr, every 10th calculation. this allows monitoring of the noise (or signal) level, to help setting an optimal squelch threshold.
• option -c: "rtl_fm -M wbfm -c 50" uses de-emphasis time constant for europe. one might also write "-c us" to use the north american 75 microSec standard. "-c eu" will use the european 50 microSec standard.
• option -v: "rtl_fm -v 1 -f 99.3M" displays verbose debug information on calculation of frequency, so that user might understand how/what frequency is tuned to.
• modulation names: found myself writing "wfm" instead of "wbfm". now the aliases are also accepted.

[hayguen]

added dc filter on raw data (after decimation) with option "-E rdc" added option "-q" for setting averaging speed for "rdc" added option "-E adc" in addition to "-E dc"

Please have a look in my mail with subject "rtl_fm: degraded demodulation caused by self-introduced DC !?" in osmocom-sdr mailing list to understand the reason for a second dc filter.

[Romeo-Golf]

Seems useful :)