added some minor options#23

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hayguen wants to merge 3 commits intosteve-m:masterfrom

hayguen:master

Commits on Jun 14, 2015

added option -L to print current level values
hayguen
committed

Commits on Jul 18, 2015

added dc filter on raw data (after decimation) with option "-E rdc"
hayguen
committed

Commits on Jul 19, 2015

"rdc" filter in rtl_fm now at capture rate, before mixing or filtering:
hayguen
committed