Added shaders examples resources

examples/resources/shaders/shapes_grayscale.fs

@@ -0,0 +1,15 @@
+#version 110
+
+uniform sampler2D texture0;
+varying vec2 fragTexCoord;
+varying vec4 fragColor;
+
+void main()
+{
+    vec4 base = texture2D(texture0, fragTexCoord)*fragColor;
+
+    // Convert to grayscale using NTSC conversion weights
+    float gray = dot(base.rgb, vec3(0.299, 0.587, 0.114));
+    
+    gl_FragColor = vec4(gray, gray, gray, base.a);
+}