allow overriding default response for failed auth
Add crossdomain decorator from http://flask.pocoo.org/snippets/56/.

This adds support for CORS in flask-RESTful.
add CORS tests
remove basestring reference
fix test
Fix attributes of FileStorage being deleted even if type is FileStorage

- Don't call .lower() and convert() if type is FileStorage
Added support for using Blueprints instead of app instances.  Tests
incomplete.
Fixed/added tests, added documentation.
Removing errant print statement...
add authors target to Makefile and generate AUTHORS.md
Potential fixes for error handling issues.
Added testcase for FileStorage type
Fixed python 2 and 3 compatibility problem
Fixed python 2 and 3 compatibility problem, again!
Added tox.ini file to use tox test tool

about tox: http://testrun.org/tox/latest/
fields.Url() should return an external URL
-Added tests to validate error routing.
-Fixed issue with error routing found with tests.
Alternative prefix handling behavior for blueprint integration.
Removed commented code blocks.
Update fields.py