Merge pull request #54 from danielquinn/patch-1

extensions should be a list, not a string.

README.md

@@ -98,7 +98,7 @@ Showdown allows additional functionality to be loaded via extensions.
 <script src="src/showdown.js" />
 <script src="src/extensions/twitter.js" />
 
-var converter = new Showdown.converter({ extensions: 'twitter' });
+var converter = new Showdown.converter({ extensions: ['twitter'] });
 ```
 
 ### Server-side Extension Usage