SlowRiot authored May 27, 2022 and freetrader committed May 27, 2022

This MR adds two new scripts:

- `contrib/bench/bench_compare.sh`:  Compare results of two benchmark runs,
  and report the biggest changes in both time elapsed and speed of execution,
  by percent, sorted by the change amount.
    - By default, reports only changes greater than 10%.
      This is configurable with the `--threshold` option.
    - Colour output is enabled by default in interactive terminals,
      disabled otherwise, controlled by both `--colour` and `--color` flags
      to allow for transatlantic flexibility ;)  Accepts "on", "off" (and
      common synonyms like "true", "false"), and "auto".
- `contrib/bench/bench_compare_branch.sh`: Check out, build and run benchmarks
   on two branches, and compare their results.
    - If one branch is specified, it compares the currently checked out
      branch against that.
    - If no branches are specified, it compares the currently checked out
      branch against master.
    - If a `--filter` argument is specified, it's passed to bench_bitcoin's
      `-filter`.
    - If `--threshold` or `--colour` arguments are specified, they are treated
      as above.
    - If one of the branches is checked out already, it builds and benchmarks
      that one first, to make best use of any cached build artefacts.
    - Example usage (basic / advanced):
        - `../contrib/bench/bench_compare_branch.sh`
        - `../contrib/bench/bench_compare_branch.sh --filter 'Base58.*' --threshold 15 master my_branch`

Test plan
---------

- ../contrib/bench/bench_compare_branch.sh master [local_branch_of_your_choice]