Added some useful postprocessing shaders

Shaders come in two flavours:
- shaders/gl330: OpenGL 3.3+ (Windows, Linux, OSX)
- shaders/gles100:  OpenGL ES 2.0 (Android, RPI, HTML5)

shaders/gl330/pixel.fs

@@ -0,0 +1,28 @@
+#version 330
+
+in vec2 fragTexCoord;
+
+out vec4 fragColor;
+
+uniform sampler2D texture0;
+uniform vec4 tintColor;
+
+// NOTE: Add here your custom variables 
+
+const float renderWidth = 1280;
+const float renderHeight = 720;
+
+uniform float pixelWidth = 5.0f;
+uniform float pixelHeight = 5.0f;
+
+void main()
+{
+    float dx = pixelWidth*(1.0/renderWidth);
+    float dy = pixelHeight*(1.0/renderHeight);
+
+    vec2 coord = vec2(dx*floor(fragTexCoord.x/dx), dy*floor(fragTexCoord.y/dy));
+
+    vec3 tc = texture2D(texture0, coord).rgb;
+
+    fragColor = vec4(tc, 1.0);
+}