add omission of comments when compressed

Author: tj

examples/media.css

@@ -1,3 +1,6 @@
+
+/* some comment */
+
 @media screen, projection {
   html {
     background: #fffef0;

index.js

@@ -49,6 +49,7 @@ Compiler.prototype.visit = function(node){
  */
 
 Compiler.prototype.comment = function(node){
+  if (this.compress) return '';
   return '/*' + node.comment + '*/';
 };