Added language and extra_request arguments (documented in README)
`extra_request` now uses querystring format as suggested by @ojii. Fallback language is now taken from the django configuration.
Documentation update
Removed custom exception handling in favor of default parse_qs one
Make override_middleware optional
code cleanup to integrate extra_request feature
Merge pull request #7 from yakky/feature/extrarequest_language

Add language extra_request parameters