[popup docs] Document new option "dismissable"

Author: Gabriel Schulhof

docs/pages/popup/options.html

@@ -47,6 +47,14 @@ <h2>Popup</h2>
 				<pre><code>$( ".selector" ).popup(<strong>{ corners: false }</strong>);</code></pre>
 			</dd>
 
+			<dt><code>dismissable</code> <em>boolean</em></dt>
+			<dd>
+				<p class="default">default: true</p>
+				<p>Sets whether clicking outside the popup or pressing Escape while the popup is open will close the popup. This option is also exposed as a data attribute: <code>data-dismissable=&quot;false&quot;</code></p>
+				<p><em>Note:</em> When history support is turned on, pressing the browser's "Back" button will dismiss the popup even if this option is set to false.
+				<pre><code>$( ".selector" ).popup(<strong>{ dismissable: false }</strong>);</code></pre>
+			</dd>
+
 			<dt><code>history</code> <em>boolean</em></dt>
 			<dd>
 				<p class="default">default: true</p>