add generateCertificate, fixes #41

[fippo]

@KaptenJansson @alvestrand
Not sure if I want to do the same for FF... maybe we should just drop support for versions < 38? Trivial to add though. cc @jan-ivar

[KaptenJansson]

Nice work! ;)

Maybe we should look over all version checks? Not sure what versions we have committed to support, be aware of Firefox ESR though which lags behind for a while, I think it's still 38.

Also having a test for this would be nice, otherwise LGTM.

[alvestrand]

That was quick :-)
Travis' hiccups seem to be a problem with fetching external content.
Should we add a function that throws a "notSupported" error when the function is not present?

[fippo]

@alvestrand code that wants to use it will have to check if that is a function anyway (if anyone is using it at all)

[KaptenJansson]

Filed #159 WRT to checking versions just to make sure we do not forget.

[fippo]

Is this only available in M49 when setting --enable-experimental-web-platform-features?
Should we do that for beta and canary? I don't want it to be an assumption we make for stable.

[KaptenJansson]

LGTM