* Modified API hackrf_is_streaming() now it returns an int HACKRF_TRUE when streaming is running.
* Added new hackrf_error especially for streaming to return more details.
* Adding management of usb transfer cancelled for hackrf_stop_rx()/hackrf_stop_tx().
* Added robustness on hackrf_close() to correctly close libusb related stuff even if USB device is removed or other problems.
* Fixed threading problems (start, stop() then start() ...).
* Cleanup the whole code.