Support measuring the cost of hooks and events

[vweevers]

Ref Level/abstract-level#45

[vweevers]

To make it easier to compare results, I added a way to collect ops/sec and print it as a table. Only for the put benchmark, to start:

$ level-bench.js run put ..\memory-level
$ level-bench.js run put ..\memory-level --events [ --put=1 ]
$ level-bench.js run put ..\memory-level-hooks --hooks [ --prewrite=1 ]
$ ...

$ level-bench plot put
benchmark put on memory-level@1.0.0 win32 x64
node@16.9.1 n=1M concurrency=4 valueSize=100B keys=random values=random

1  memory-level#hooks                      36588 ops/s ±8.51%  fastest
2  memory-level#main                       35837 ops/s ±8.12%   +1.70%
3  memory-level#hooks  hooks.prewrite=1    35286 ops/s ±6.51%   +1.75%
4  memory-level#main   events.put=1        35508 ops/s ±7.47%   +2.01%
5  memory-level#hooks  events.write=1      34692 ops/s ±6.83%   +3.69%
6  memory-level#hooks  hooks.prewrite=100  34302 ops/s ±8.28%   +6.05%