This is a proof of concept, for moving the benchmark suite to use
[nanobench](https://github.com/martinus/nanobench.git), which is a
single header file but gives some great advantages over the existing
benchmark suite:
* Robustness - nanobench will explicitly tell you when benchmarks are
unstable, and offer some guidance to help stabilise them.
* JSON Output - this should allow us to store the results in a more
machine friendly format, in future we can integrate this into CI to do
checks on PRs