Fetch embedded resources

[mattgrill]

Fetch embedded resources from a JSON document returned from Drupal. This should address some of the requests in #22

[coveralls]

Coverage remained the same at 100.0% when pulling d44fdd2 on fetch-embedded into 1e4721f on 0.7.0.

[coveralls]

Coverage remained the same at 100.0% when pulling e071b56 on fetch-embedded into 1e4721f on 0.7.0.

[infiniteluke]

A comment about not wanting to fetch the same resource multiple times hence the use of Set could help future contributors. Also a note about Promise.all needing an array. ??

[infiniteluke]

This is awesome! 🎉

[mattgrill]

@infiniteluke 👍

[coveralls]

Coverage remained the same at 100.0% when pulling 5032fa5 on fetch-embedded into 1e4721f on 0.7.0.

[coveralls]

Coverage remained the same at 100.0% when pulling 81822e2 on fetch-embedded into 1e4721f on 0.7.0.

[prestonso]

LGTM