move shaders into .glsl files and add #include feature

data/shaders/include/rand.glsl

@@ -0,0 +1,10 @@
+// http://byteblacksmith.com/improvements-to-the-canonical-one-liner-glsl-rand-for-opengl-es-2-0/
+highp float rand(mediump vec2 co)
+{
+    highp float a = 12.9898;
+    highp float b = 78.233;
+    highp float c = 43758.5453;
+    highp float dt= dot(co.xy, vec2(a,b));
+    highp float sn= mod(dt, 3.14);
+    return fract(sin(sn) * c);
+}