Hope add a new function, achieve search through the coverage rate of matching quantity.

[wilon]

Such as func FindCoverageRate(bitmap, source_bitmap robotgo.CBitmap, tolerance float64, rate float64) (int, int)

bitmap => Needle 2x3
source_bitmap => Haystack 5x4
tolerance => 0.1
rate => 0.5, same as 50%

From the first w violent match, Until match four b, 4/6 > 50%, return (3, 1)

		/* TODO: The above commented out code fails at certain edge cases, e.g.:
		 * Needle: [B, b
		 *          b, b,
		 *          B, b]
		 * Haystack: [w, w, w, w, w
		 *            w, w, w, w, b
		 *            w, w, w, b, b
		 *            w, w, w, w, b]
		 * The previous algorithm noticed that the first 3 x 3 block had nothing
		 * in common with the image, and thus, after scanning the first row,
		 * skipped three blocks downward to scan the next (which didn't exist,
		 * so the loop ended). However, the needle was hidden IN-BETWEEN this
		 * jump -- skipping was appropriate for scanning the column but not
		 * the row.
		 *
		 * I need to figure out a more optimal solution; temporarily I am just
		 * scanning every single y coordinate, only skipping on x's. This
		 * always works, but is probably not optimal.
		 */

/* TODO: The above commented out code fails at certain edge cases, e.g.: