Remove unused pnUtTime functions.
std::chrono-ize hsTimer.
Template-ize hsTimer return values.
Work towards killing TimeGetMs.

Only remaining uses are in pnAsyncCore stuff, and I'm not touching that
until the std::thread merge is figured out.
Always use hsTimer for profile stats.

This fixes the weird flickering and inaccurate numbers that were showing up on Windows.
Merge pull request #418 from dpogue/timer

std::chrono hsTimer