Add informative parameters to 'RateLimited' Exception

[AlonFasta]

@jsocol in order to allow proper differentiation and documentation in case of multiple rate limit decorators on a single Django view, i have added 'key', 'group' and 'rate' details to 'RateLimited' Exception, WDYT?

Thanks :)

[AlonFasta]

@jsocol Any feedback?

[aambrozkiewicz]

Hey, I had similar idea but I would say than instead of passing individual parameters, why not pass what get_usage returns? This way people might use the additional information like time_left as part of the response.

Let me know, I can prepare a PR.