Add support for profiling tools

[Firehed]

Exactly how this should work is a bit up in the air. At minimum, I think the following is required (names TBD):

interface Profiler
{
  public function startEvent(string $name, string $description = '');
  public function endEvent(string $name);
}

And then allow the dispatcher to fire events before and after the actual endpoint execution. Implementations should be responsible for tracking durations, etc. I know this would generally work for Clockwork, but I'm not sure if that interface is generic enough to work with additional tools (importantly, ones that are better-suited to profiling APIs)

[Firehed]

My general take is that this is mostly now achievable with Middleware without the need to do further framework modification, but I'm going to leave this open in case any interesting ideas come up.