Add unit tests for AssociationDict
Adds support for AssociationDict type for POST

The issue is that AssociationDict type does not have an `append` method
Fixes typo for association
Fixes newlines and quote type
Fixes superflous newline
Merge branch 'assoc-proxy' of github.com:Svenito/flask-restless into assoc-proxy
Removes extraneous spaces.
Records change due to previous commits.