Ec3k

* Implemented CRC check for received packets.
* Frequency, rtl-sdr device and other settings can be set in
EnergyCount3K constructor.
* Added device_on_flag and reset_counter fields to EnergyCount3KState.
* Renamed fields in EnergyCount3KState object (old names remain as
aliases for backwards compatibility with 1.0.x)
* Update for GNU Radio 3.7.0 compatibility.

* Fix "output 1 is not connected internally" error when using
gr-osmosdr versions v0.1.1 and later

* Better clean-up of threads.
* Less verbose capture.py by default.

* First release