Support for "inline" multiple inheritance

[DavideRossi]

types:
  A:
  B:
  C:
    type: [A, B]

/foo:
  post:
    body:
      type: [A, B]

is not supported (I'm guessing since it produces erroneous code) whereas

    body:
      type C

is.

Maybe this is a duplicate of #245?

[jpbelang]

I've build a patch which might get me closer to better code, actually. Check please :-)

This is the last issue before release. Type generation will move to a separate project for the next release.