add shot reload overlay bar

assets/fs/shaders/overlay_reload.f.glsl

@@ -0,0 +1,7 @@
+
+varying vec3 pos_i;
+
+void main(void)
+{
+    gl_FragColor = mix(vec4(.7, .7, 1, 1), vec4(0, 0, 1, 1), (pos_i.x + 1) / 2);
+}