Access to performance within a benchmark

**Description**
I'd really like to be able to easily check benchmark times as part of CI, to catch unwanted performance regression.

Within the context of BENCHMARK, i'd like 2 features:

1. The ability to assert meter time below some value _for each iteration_. THis would enable me to ensure that a latency has never been exceeded.

2. The ability to assert the mean is below some value

If these can be achieved with existing machinery, then I'd like them clearly added to the docs, because its none obvious how to achieve these aims.