Per-template profiling/timing

[jeremydw]

Over time, some templates may incur more of a performance hit than others. Because our core is so optimized, as sites grow complicated templates will have the largest impact on performance.

Hugo has a nice feature that shows a table of which templates get rendered, their timings, and the number of times the template is rendered. A similar feature would be useful to have in Amagaki:

https://gohugo.io/troubleshooting/build-performance/