LibHTML: Handle comments in the CSS parser

Turn consume_whitespace() into consume_whitespace_or_comments() and
have it swallow /* comments */ as well.

Base/home/anon/www/welcome.html

@@ -4,10 +4,15 @@
 <title>Welcome!</title>
 <!-- this is a comment -->
 <style type="text/css">
+/* css comment */
 body {
     background-color: #fff;
-    color: #000;
+    color: #000; /* another css comment */
 }
+/* lol
+   a
+   css
+   comment */
 h1 {
     color: #800;
 }