Support text/json+oembed (Soundclound)

[Avnerus]

Hi,
I tried to embed a Soundcloud link and the the oEmbed directive was not found.
I noticed that they use the typetext/json+oembed instead of application/json+oembed.
After applying the following fix, Soundcloud embedding works.

/Avner

[zerocrates]

I assume there's no chance of Soundcloud changing things on their end...

It's a little annoying to be dealing with a very short spec like oEmbed that specifically says

The type attribute must contain either application/json+oembed for JSON responses, or text/xml+oembed for XML.

but to encounter something like this anyway.

[zerocrates]

On the other hand we already accept link rel "alternative" here so I suppose there's no need to stand on strict correctness and I can't see it harming anything, so I merged it.

Thanks for your contribution.