move shaders into .glsl files and add #include feature

data/shaders/uvs.glsl

@@ -0,0 +1,18 @@
+[[vertex]]
+uniform mat4 mvp;
+in vec4 pos;
+in vec2 uvs;
+out vec2 uv;
+void main()
+{
+    uv = uvs;
+    gl_Position = mvp * vec4(pos.xyz, 1.0);
+};
+
+[[fragment]]
+in mediump vec2 uv;
+out mediump vec4 frag;
+void main()
+{
+   frag = vec4(uv, 0.0, 1.0);
+};