Clear API (#274)

* blockManager.clear

* upd

* api bez ebanoj knopki api

* fix assignment

* insert empty block with clear method

* clear and render methods improved

* open saver.save()

* add comments

* update comments

* fix data returned by editor

example/example.html

@@ -104,6 +104,8 @@
 
     console.log('Editor instance:', editor);
 
+    window.editor = editor;
+
 //    var editor2 = new CodexEditor({
 //        holderId : 'cdx',
 //        initialBlock: 'header'