Clean Up Documentation for Issue 28

[cpiggott]

All models are name-spaced to DwollaSwagger\models meaning all the PHPDocs are incorrect that use @return <MODEL>.

This updates the documentation to show the correct return type.

[randaleWatson]

If the conflicts with master can be fixed this would be a good PR as I am having to write doc comments a bunch to get type hint to work and some of the return types are wrong current like TransApi->create() I think returns a url string but current doc says it returns a unit.
Way off is FundingApi->createCustomerFundingSource() it's return type us a whole FundingSource but I think it returns only url for said funding source.
almost all the create methods need to be updated to accept an array | CreateXXXModel so type should be remove from parameters and just hinted in the phpDocs.