Extends support array of objects too

[rogerleite]

This patch allows a schema extends many objects as necessary.
More details at test files.

[rogerleite]

Hey @hoxworth, you need help with all these pending pull requests? I can help.

[hoxworth]

Sorry for taking so long to get back to you @rogerleite - I like this feature as it duplicates the allOf feature of draft-04. I have slight concerns in that schemas that utilize this functionality will not pass validation against draft-03/schema, but that should be understood as it is extended functionality and does not break existing schemas. I'll merge this shortly.

[rogerleite]

Thanks @hoxworth!