Add selector computation timings to JSON output

[timminata]

Awesome library!
It would be really great if there was a way to time all registered selectors. We also use selectors a lot, and, although the graph from reselect-tools is really helpful, it would be great to be able to track time spent computing each selectors output. Is there any easy way to achieve this? I'd be happy to try make a PR if you point me in the right direction. Unless there is already something out there.
Thanks!