calibration: handle KeyboardInterrupt
test: fix audio filenames
ignore sent/received audio/data files
reorganize directory structure
remove unused code
move bash scripts
test.sh: default directory should be $PWD
config: allow command line modem configuration
send: fix prefix generation
test.sh: save data and audio files into `test_results` directory.
test: add simple full test via identity channel
test: add noisy channel support