Add PhyWhisperer backend.

[jpcrypt]

No description provided.

[ktemkin]

This code seems good (nice and minimal, too). In testing, I was able to get short captures working, but I haven't had luck with --size 0 / continuous captures. I suspect the relevant changes to get that working well will need to be in phywhisperer, though, and not here.

Either way, there's at least one blocking thing that needs to be fixed (the import issue mentioned in comments) before this can be merged; and few other comments that you might want to address. Should be a quick merge after that. :)

[jpcrypt]

Thanks for the review! Yeah size=0 is work-in-progress on the PhyWhisperer side, it's intended for stream capture which isn't working yet.

[ktemkin]

Finally getting around to testing the updated changes; sorry for the delay. :)

[ktemkin]

This seems to work; so merging it as a baseline. :)

Thanks!