add more is-* functions

test/css/functions.css

@@ -34,6 +34,9 @@
   keyword: true;
   number: true;
   string: true;
+  pixel: true;
+  percent: true;
+  em: true;
 }
 #alpha {
   alpha: rgba(153, 94, 51, 0.6);

test/less/functions.less

@@ -38,6 +38,9 @@
     keyword: is-keyword(hello);
     number: is-number(32);
     string: is-string("hello");
+    pixel: is-pixel(32px);
+    percent: is-percentage(32%);
+    em: is-em(32em);
   }
 }