Introduction of rate limits

[mihalt]

Continue of #275

I plan to introduce https://pyratelimiter.readthedocs.io/en/latest/ to my project to avoid api exceptions. I've checked your section https://skpy.t.allofti.me/background/authentication.html#rate-limiting and don't have any descriptions of exact limits ranges. I understand that you can't give me exact numbers, because you are not a skype developer, but approximate numbers by your expirence would be very helpfull. How much requests should I send in an hour, a day, a week, a month? What limits are pessimistic and should exactly work and what limits are optimistic and just to try?