Convert 'x-*' security types to 'apiKey'

[bpedro]

Convert any security types starting with x- (see https://github.com/raml-org/raml-spec/blob/raml-10/versions/raml-10/raml-10.md#security-scheme-types , x-{other}) to apiKey (see http://swagger.io/specification/#securitySchemeObject , type).

Why?

Because many RAML definitions use x- security types and the converter would crash on those.

[IvanGoncharov]

@bpedro Thank you for PR.
But you made only a first step, you need to also add name and in properties, see this.
You can get this info from discribedBy.

RAML also support multiple keys passed to API and it can be converted in Swagger 2.0
But it pretty complicated construction so for a first version it can be checked using assert.

It will be great if you complete this PR if not I can finish it for you this week.

Note: currently I don't support RAML 1.0 only 0.8
It looks like 1.0 is backward-compatible but I need to check it.

[MikeRalphson]

Hi @bpedro sorry to dig this up, but are you still interested in progressing this PR? No problem if not.