Removed the subentity_type field and converted it to a subentity_kind field in the migrations. Performed two schema migrations so that other apps can easily write a data migration
updated models tests
bumped version
updated docs to remove references to subentity types
bumped django entity req
updated docs to let users know they are responsible for writing the data migration between entity types and entity kinds
Merge pull request #8 from wesleykendall/develop

Entity Subscriptions use Entity Kinds instead of Entity Types