move shaders into .glsl files and add #include feature

data/shaders/font.glsl

@@ -0,0 +1,22 @@
+[[vertex]]
+uniform mat4 mvp;
+in vec2 pos;
+in vec2 uvs;
+out vec2 uv;
+void main()
+{
+   uv = uvs;
+   gl_Position = mvp * vec4(pos, 0.0, 1.0);
+};
+
+[[fragment]]
+uniform mediump sampler2D tex;
+uniform mediump vec4 col;
+in mediump vec2 uv;
+out mediump vec4 frag;
+void main()
+{
+   mediump float a = texture(tex, uv).r;
+   frag = vec4(col.rgb, a);
+};
+