Basic flask.Blueprint support for flask_restuful.Api

Adjusted flask_restful.Api so it can now transparently accept a flask.Blueprint in place of a flask.Flask object.  Blueprints containing Apis are limited to single registration (a valid behavior according to the Blueprint documentation).  The Api also resolves url prefix conflicts between the Blueprint, the Api, and any prefix provided at Blueprint registration; at Api initialization, if a Blueprint is provided, if either the Api or Blueprint has a prefix set, or the both have the same prefix set, they are both set to use that prefix, with mismatching prefixes raising an exception; when the Blueprint is registered to an app, if a prefix was provided in the registration options, it overrides any existing prefix on either the Blueprint or the Api.