Add options stats_interval and stats_interval_opts to allow interval based stats
printing. This provides an easy way to collect stats without code changes,
because opt.stats_print may not work (some binaries never exit).
JSON format is largely meant for machine-machine communication, so
adding the option to the emitter. According to local testing, the
savings in terms of bytes outputted is around 50% for stats printing
and around 25% for prof log printing.
- Make API more clear for using as standalone json emitter
- Support cases that weren't possible before, e.g.
- emitting primitive values in an array
- emitting nested arrays
The emitter can be used to produce structured json or tabular output. For now
it has no uses; in subsequent commits, I'll begin transitioning stats printing
code over.
