improved atimport() for other at-rules. ex)@charset

Author: elegantcoder

test/cases/charset.css

@@ -0,0 +1,2 @@
+@charset "UTF-8";       /* Set the encoding of the style sheet to Unicode UTF-8*/
+@charset 'iso-8859-15'; /* Set the encoding of the style sheet to Latin-9 (Western European languages, with euro sign) */

test/cases/charset.json

@@ -0,0 +1,12 @@
+{
+  "stylesheet": {
+    "rules": [
+      {
+        "charset": "\"UTF-8\""
+      },
+      {
+        "charset": "'iso-8859-15'"
+      }
+    ]
+  }
+}