add ability to rate limit after X errors in X minutes

[tikotzky]

slack will disable the integration if it starts sending too many errors too quickly
see: https://api.slack.com/docs/rate-limits

we should probably add an option to which allows you to specify the max messages/time and it should auto rate limit once that limit is reached.

[tikotzky]

@eligolding wanna take a crack at this?

[tikotzky]

idea would be to throttle this call so we dont end up clobbering slack if something goes 💣

[gictor]

We had some issues with this causing our application to hogg all the memories. Suggested fix

64ca7b9

[gictor]

I saw that the automatic tests didn't go through, now its backwards compatible #14