Embedding in subdocuments

It’s possible now to embed documents by references located in
subdocuments using dot notation.
For example, it’s possible to make the query:
?embedded={“user.friends”:1} for a document which have “user”
subdocument with list of references “friends”.
Merge branch 'reference-embedding-in-subdocuments' of github.com:hmbg/eve into hmbg-reference-embedding-in-subdocuments
Update 'subdocument embedding' docstrings to 0.5

Support for embedding documents located in subdocuments has been merged
into 0.5-dev instead of 0.4, so docstrings from original PR needed an
update.
Changelog: Embedding of referenced documents. #389.
Dmitry Anoshin
Merge branch 'hmbg-reference-embedding-in-subdocuments' into develop