Zephyr HCI USB firmware with TX power vendor commands

[mogenson]

I'm uploading a firmware binary here, because I think I can link to it from a new mkdocs page from this PR: #258

hci_usb.zip

[barbibulle]

The current setup is that the contents of the GitHub pages are loaded from the special gh-pages branch of the repo, which contains only the output of MkDocs. MkDocs has a built-in facility for updating this branch after building the docs. One option may be to add the zip file to a subdir of docs/src (maybe docs/src/downloads/zephyr). It's no ideal that it would live under docs, because it's not a doc, but it's still an Ok option I think. I've pushed PR #276 as a way to do that if you think that works.

[mogenson]

Sure that works for me. I didn't know if you wanted that binary committed as part of the git repo or not.