Fix string const-ness
`linkForRel:` origin
Fix swapped constructBodylessHTTPRequestForAction for constructHTTPRequestForAction
Embedded entities `rels` origin

- Load embeded entities including their `rels`
- Query entities for `rels` when looking for a link
- Prefer using embeded entities in `stepToLinkRel:`
Merge pull request #6 from zdne/master

embedded entity relations & use / bug fixes