Add option for using requests/min in addition to requests per second. Also a Check for avgresponse time.

[cirej2000]

For those of us with lower traffic services, it would be helpful to have the option of expressing our throughput in requests/minute vs requests/second and have that be a better scale for showing requests. Especially when it's less than 60 RPM.

Also would be great to have AvgResponseTime be a check.

I've coded this up and just need to update the tests and this could be ready for a pull requests in the next 24 hours.