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/cross_hatching.fs

@@ -0,0 +1,44 @@
+#version 330
+
+in vec2 fragTexCoord;
+
+out vec4 fragColor;
+
+uniform sampler2D texture0;
+uniform vec4 tintColor;
+
+// NOTE: Add here your custom variables 
+
+float hatchOffsetY = 5.0f;
+float lumThreshold01 = 0.9f;
+float lumThreshold02 = 0.7f;
+float lumThreshold03 = 0.5f;
+float lumThreshold04 = 0.3f;
+
+void main()
+{
+    vec3 tc = vec3(1.0, 1.0, 1.0);
+    float lum = length(texture2D(texture0, fragTexCoord).rgb);
+
+    if (lum < lumThreshold01) 
+    {
+        if (mod(gl_FragCoord.x + gl_FragCoord.y, 10.0) == 0.0) tc = vec3(0.0, 0.0, 0.0);
+    }
+
+    if (lum < lumThreshold02) 
+    {
+        if (mod(gl_FragCoord .x - gl_FragCoord .y, 10.0) == 0.0) tc = vec3(0.0, 0.0, 0.0);
+    }
+
+    if (lum < lumThreshold03) 
+    {
+        if (mod(gl_FragCoord .x + gl_FragCoord .y - hatchOffsetY, 10.0) == 0.0) tc = vec3(0.0, 0.0, 0.0);
+    }
+
+    if (lum < lumThreshold04) 
+    {
+        if (mod(gl_FragCoord .x - gl_FragCoord .y - hatchOffsetY, 10.0) == 0.0) tc = vec3(0.0, 0.0, 0.0);
+    }
+
+    fragColor = vec4(tc, 1.0);
+}