Add support for Doctrine Embeddables

[regniblod]

I'm using Doctrine Embeddables in a project but they don't work as expected.

I tried to fetch a resource without adding the embeddables as relationships, but they just don't appear in the response - it works, just that the fields are not present, like if they were not included.

If I add the embbedables as relationships it fails because it tries to join with the non-existent table for the embbedable.