Webauthn support (#11)

Remove outdated dev-dependencies (#27)

Treat cid_pubkey as optional (#20)

This resolves #14, which became necessary due to a change in newer versions of Chrome.

Note: Chrome now seems to attach garbage attestation certificates, at least on the hardware I tested with. This means that full CA verification may fail even when everything else is correct. There were several changes around the CryptoToken extension/implementation in [Chrome 74](https://chromium.googlesource.com/chromium/src/+log/73.0.3683.103..74.0.3729.108?pretty=fuller&n=10000) (warning: slow) so this is likely a regression of some kind, and may be specific to certain OSs (my testing was on macOS 10.14)

Add travis build config