move shaders into .glsl files and add #include feature

data/shaders/color-tri.glsl

@@ -0,0 +1,21 @@
+[[vertex]]
+uniform mat4 mvp;
+in vec4 pos;
+in vec2 uvs;
+out vec3 uv;
+void main()
+{
+   gl_Position = mvp * pos;
+   uv = vec3(uvs, pos.w);
+};
+
+[[fragment]]
+#include "include/hsv.glsl"
+uniform mediump vec4 col; // in HSV
+in mediump vec3 uv;
+out mediump vec4 frag;
+void main()
+{
+   mediump float sat = tan(atan(uv.y, uv.x)) * 0.5 + 0.5;
+   frag = vec4(hsv2rgb(vec3(col.r, sat, uv.x)), 1.0);
+};