Added a "brightness boost" feature for the shadow mask that works by making the brightness ratio between bright and dark mask pixels closer to 1 for the brighter parts of the image.
Added clamping to zero so that underscanning produces a black border.
Added a "raster bloom" effect to crt-geom-deluxe that makes the image grow slightly when the average brightness of the screen is high, mimicking a common defect in CRTs.
This includes several aperture grille / shadow mask patterns. Note that these are all designed to be used on a display with RGB subpixel order, and may thus suffer if rotated or used with a BGR display.
