Experimental windowed score functions.

This adds "Windowed" and "Windowed Strict" score modes, that can be selected from the Developer page.

Windowed = the best score over a 10% window of samples, reaching 90% or more of the target framerate.
Windowed Strict = the best score over a 10% window of samples, searching from lowest-to-highest complexity, that never drops below 90% of the target framerate.

A comparison of ramp scores:

Slope

Windowed

Windowed Strict

Overall Windowed Strict looks the most promising as far as giving stable, and explainable results.