Added initial CachedReferenceField
fixes for rebase branch
added CachedReferenceField restriction to use in EmbeddedDocument
refs #709, added CachedReferenceField.sync_all to sync all documents on demand
refs #709, fix typos
refs #709, added support to disable auto_sync
fixes for python2.6
added documentation about CachedReferenceField
Update README.rst
Merge pull request #718 from mbalasso/patch-1

Update README.rst
Fixed typo.
Merge pull request #720 from pashadia/master

Fixed typo.
small fixes for python2.6
Merge pull request #709 from wpjunior/cached-reference-field

CachedReferenceField implementation
fix-#399: Not overriding default values when loading a subset of fields
fix-#620: saving document doesn't create new fields in existing collection
Merge pull request #723 from DavidBord/fix-620

Fix 620
Update changelog.rst
fix-#725: queryset delete() should return the number of deleted objects
Added PyPy3 to the build matrix.