Implement rate limiting

[mnederlof]

Rate limiting is implemented by responding with HTTP 429.

Feature probably does not work within listen section, so currently only implemented in frontend/backend scenario. Also updated the template for *-end sections, so options are properly handled, by using a blacklist for options.

Tests and readme is updated to highlight required configuration options.

[mnederlof]

I chose a blacklist, so new options are still usable, when using a newer version than 1.6 (which is what i based the blacklist on)

[fpytloun]

Thank you