Implement animated flash tiles in Tilemap

Flash tiles start with an alpha of 60, which ramps up to 120
in 16 frames and 4 steps, then ramps down again over the same period.

shader/flashMap.frag

@@ -0,0 +1,13 @@
+
+uniform float alpha;
+
+varying vec4 v_color;
+
+void main()
+{
+	vec4 frag = vec4(0, 0, 0, 1);
+
+	frag.rgb = mix(vec3(0, 0, 0), v_color.rgb, alpha);
+
+	gl_FragColor = frag;
+}