Support for compressed archives

[Teque5]

Back when this repo was the spec, we considered it out-of-scope to handle the compression side, but I think if we wanted we could support .sigmf.7z and .sigmf.zip files with this module. If anyone thinks this is a good idea I can work up a PR.

[aromanielloNTIA]

This would be an excellent addition!

[Teque5]

For my own reference this can easily be done with our existing implementation using tarfile.TarFile which should allow x.sigmf.gz, x.sigmf.bz2, and x.sigmf.xz.

To allow x.sigmf.zip I believe we would need to use the similar zipfile.ZipFile object.

To allow x.sigmf.7z I see there is py7zr.SevenZipFile although I need to investigate further.