Data-attribute: noted data-iconshadow as deprecated

Closes gh-265
Fixes gh-264

Author: agcolom

pages/data-attribute.html

@@ -27,7 +27,7 @@ <h2><a href="../button/">Button</a></h2>
 	</tr>
 	<tr>
 		<th>data-iconshadow</th>
-		<td><strong>true</strong> | false</td>
+		<td>true | <strong>false</strong> <span class="warning">Deprecated as of 1.4.0 and will be removed in 1.5.0.</span></td>
 	</tr>
 	<tr>
 		<th>data-inline</th>