Converter for Signal Hound Recordings

[Teque5]

Originally discussed in #23, we want to implement a converter for recordings made by Signal Hound RF recorders.

• Use CLI sigmf_convert entry point and use sigmf.convert.hound.hound_to_sigmf() as entry point.
• Use sigmf.fromfile() entry point and file extension or XML parsing detection method.
• Support --archive and --ncd modes if possible
• Use example recordings in nonsigmf examples repo in test_convert_hound.py
• Add to converters.rst in Documentation

Signal hound appears to be a detached format with a pair of (.iq and .xml) so the converter will take the xyzbca.xml as the input.