Merge pull request #2 from darrinm/master

repair mismatched setting names (ALLOWED -> ALLOW)
increment version number to v0.03
include allow-credentials in simple requests
fix Access-Control-Allow-Credentials defaults in README and add changelog
fix README.md formatting
fixed #3 by intercepting CORS preflight requests and creating an empty response for it
update README
Merge branch 'master' of https://github.com/OttoYiu/django-cors-headers