Scrape Rate Limits from Docs

[jonthegeek]

I added the rate limits for the functions we specifically call out in slackcalls (in internal data as rate_limits_known). It would be helpful to scrape the method docs to grab all of them, so we don't have to think about them. I allow people to override them (in case they want to experiment with the "burst" options the docs talk about), but for the most part they really should just work.

[yonicd]

I think this page should be good for that info? https://api.slack.com/docs/rate-limits

[jonthegeek]

Those are the levels, and I built them in so we can update them in one place (in data-raw), but each endpoint lists a level in its docs.