add support for OpenMetrics message format

[aparcar]

This commit adds support for the OpenMetrics message format1 which is equivalent to the message format of Prometheus. Its advantage is to be easily human readable as well as consumable by time series databases.

Lastly it's possible to display results directly within the GitLab CI.

It's now possible to pass 'openmetrics' as a message format, an example is shown below:

criterion_benchmark_result_ns{id="address_scan",confidence="estimate",input_size="4",aggregation="slope"} 33811.02693018697
criterion_benchmark_result_ns{id="address_scan",confidence="upper_bound",input_size="4",aggregation="slope"} 35170.884432780265
criterion_benchmark_result_ns{id="address_scan",confidence="lower_bound",input_size="4",aggregation="slope"} 32402.287415202973
criterion_benchmark_info{id="address_scan",input_size="4",report_directory="/path/criterion/reports/address_scan/4"} 1

Closes: #54

Signed-off-by: Kevin Becker [email protected] Signed-off-by: Paul Spooren [email protected]

[aparcar]

@bheisler please approve the CI

[aparcar]

Friendly ping

[bheisler]

Thanks for the pull request, and the patience! Those errors look unrelated to your changes, so I'll try and fix them and re-run the checks.

[bheisler]

OK, this looks good. Thanks for the pull request!