Ben Cumming authored 7 years ago and Sam Yates committed 7 years ago

Replace the profiler with a simpler design that works for nested multi-threaded regions.

* Replace hierarchical profiler accounting with strictly exclusive regions.
* Make tree grouping of profile data a presentation concern.
* Uncouple profiler semantics from Arbor classes such as `model`.
* Add thorough documentation for the new profiler to the library documentation.