Consider adding yaml tags on Config struct

[sunshinekitty]

Currently there are just json tags, this is not an issue with github.com/ghodss/yaml since it does yaml -> json before unmarshalling, but if you're not using this package you will find things don't unmarshal correctly.

[JorritSalverda]

I tested locally with the yaml tags, but with gopkg.in/yaml.v2 it fails to unmarshal certificate-authority-data into a []byte. So it's not as simple as just adding the tags.

With github.com/ghodss/yaml@v1.0.0 and no yaml tags it worked fine though.

[ericchiang]

#71 has been merged