add shot-ring shader and create shot-ring attributes buffer

assets/fs/shaders/shot-ring.f.glsl

@@ -0,0 +1,5 @@
+
+void main(void)
+{
+    gl_FragColor = vec4(1.0, 0.1, 0.1, 1.0);
+}

assets/fs/shaders/shot-ring.v.glsl

@@ -0,0 +1,13 @@
+
+uniform mat4 projection;
+uniform mat4 modelview;
+uniform float scale;
+
+/* pos.xyz is position, pos.w is offset */
+attribute vec4 pos;
+
+void main(void)
+{
+    vec3 pos3 = pos.xyz * (scale + pos.w);
+    gl_Position = projection * modelview * vec4(pos3, 1);
+}