init commit, with sample code

SFML/examples/shader/resources/blink.frag

@@ -0,0 +1,9 @@
+uniform sampler2D texture;
+uniform float blink_alpha;
+
+void main()
+{
+    vec4 pixel = gl_Color;
+    pixel.a = blink_alpha;
+    gl_FragColor = pixel;
+}