Add benchmark performance tests

[James Navin]

More users are asking for performance improvements in order to use the validator library in production environments.

In order to better make decisions about what changes will have positive performance improvements it would be useful to have a set of micro benchmarks / performance tests that can be executed to measure performance changes.

Suggest something like https://openjdk.java.net/projects/code-tools/jmh/ be used.

[James Navin]

Available in v2.11.2