Add support for dithering and fixed wait times between requests

[GlenTiki]

This would need to be specified as a range for dithering effects and a fixed number for fixed waits.

Dithering would mean waiting a random amount time within the range specified to make the next request.

Fixed waits is waiting a fixed amount time between requests.

The use case is to add "down" times between requests. This is useful to generate more "real-world" like usage.

[marianofino]

Hi @GlenTiki, is fixed waits the same as #174 ?