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/predator.fs

@@ -0,0 +1,27 @@
+#version 330
+
+in vec2 fragTexCoord;
+
+out vec4 fragColor;
+
+uniform sampler2D texture0;
+uniform vec4 tintColor;
+
+// NOTE: Add here your custom variables
+
+void main()
+{
+    vec3 color = texture2D(texture0, fragTexCoord).rgb;
+    vec3 colors[3];
+    colors[0] = vec3(0.0, 0.0, 1.0);
+    colors[1] = vec3(1.0, 1.0, 0.0);
+    colors[2] = vec3(1.0, 0.0, 0.0);
+    
+    float lum = (color.r + color.g + color.b)/3.0;
+    
+    int ix = (lum < 0.5)? 0:1;
+    
+    vec3 tc = mix(colors[ix], colors[ix + 1], (lum - float(ix)*0.5)/0.5);
+    
+    fragColor = vec4(tc, 1.0);
+}