[addon attach] Fix reference error

Also bump version to 0.21

addons/attach/attach.js

@@ -33,10 +33,10 @@
         socket.send(data);
       };
 
-      socket.addEventListener('message', _getMessage);
+      socket.addEventListener('message', term._getMessage);
 
       if (bidirectional) {
-        this.on('data', _sendData);
+        this.on('data', term._sendData);
       }
       
       socket.addEventListener('close', term.detach.bind(term, socket));

bower.json

@@ -1,5 +1,5 @@
 {
   "name": "xterm.js",
-  "version": "0.20",
+  "version": "0.21",
   "ignore": ["demo", "docs", "test", ".gitignore"]
 }

docs/conf.py

@@ -51,9 +51,9 @@ copyright = u'2014, SourceLair Limited'
 # built documents.
 #
 # The short X.Y version.
-version = '0.20'
+version = '0.21'
 # The full version, including alpha/beta/rc tags.
-release = '0.20 Alpha'
+release = '0.21 Alpha'
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.