hackrf_sweep: removed bin width from binary output because a more precise result can be computed from the number of bins in a record

Reenable some clocks so that HackRF boots

hackrf_sweep: fftwf_free

clarified some things in firmware/README

Power down or disable all clocks that we aren't using

added fields to hackrf_sweep binary output

Modify hw sync mode to require an argument

Disable EMC clock

fixed bug in frequency reported to binary output of hackrf_sweep

hackrf_transfer: switched some output messages from stdout to stderr