Support for SIMD operations for RGG1555

Description

Up to 3x the performance for RGG1555 with SIMD operations. The current implementation is hardcoded for 16 bytes at a time (128 bits). Still requires some testing and validation for AVX2 and AVX512.

Fixes #45 (closed)

src/color.rs

@@ -262,8 +262,9 @@ mod tests {
             000, 000, 255, // Blue
             255, 255, 000, // Yellow
             255, 000, 000, // Red
+            020, 020, 200, // Blueish
         ];
-        let mut rgb1555_pixels: Vec<u8> = vec![0; 34];
+        let mut rgb1555_pixels: Vec<u8> = vec![0; 36];
 
         rgb888_to_rgb1555_scalar(&rgb888_pixels, &mut rgb1555_pixels);
 
@@ -285,6 +286,7 @@ mod tests {
             0b00011111, 0b10000000, // Blue
             0b11100000, 0b11111111, // Yellow
             0b00000000, 0b11111100, // Red
+            0b01011001, 0b10001000, // Blueish
         ];
 
         assert_eq!(rgb1555_pixels, expected_rgb1555);
@@ -313,8 +315,9 @@ mod tests {
             000, 000, 255, // Blue
             255, 255, 000, // Yellow
             255, 000, 000, // Red
+            020, 020, 200, // Blueish
         ];
-        let mut rgb1555_pixels: Vec<u8> = vec![0; 34];
+        let mut rgb1555_pixels: Vec<u8> = vec![0; 36];
 
         rgb888_to_rgb1555_simd(&rgb888_pixels, &mut rgb1555_pixels);
 
@@ -336,6 +339,7 @@ mod tests {
             0b00011111, 0b10000000, // Blue
             0b11100000, 0b11111111, // Yellow
             0b00000000, 0b11111100, // Red
+            0b01011001, 0b10001000, // Blueish
         ];
 
         assert_eq!(rgb1555_pixels, expected_rgb1555);