Performance stats

This patch also contains the changes from !1131 (closed), so that should probably be closed.

This patch adds the perfstats command, which shows various performance measurements of the game engine.

perfstats 1 shows rendering related information. (Formerly renderstats. The labels and text size have been changed to be much clearer.)

Software:

OpenGL:

perfstats 2 shows game logic related information.

The columns on the left and the red batch measurements in the screenshots above are time measurements, and the rest of the numbers are counters.

perfstats 3 measures the time taken by Lua ThinkFrame hooks.

(All time measurements are in microseconds)

On resolutions smaller than 640x400, the text is drawn in the old renderstats style with the additions from !1131 (closed). (Thanks Golden!) The ThinkFrame screen is not implemented for low resolutions because there is less room for text.