docs(): updated

docs/VERSION

@@ -1 +1 @@
-3.0.0
+4.0.0

docs/sources/versions.html_fragment

@@ -1,3 +1,4 @@
+<li><a class='version' href='/v3.0'>Version v3.0</a></li>
 <li><a class='version' href='/v2.6'>Version v2.6</a></li>
 <li><a class='version' href='/v2.5'>Version v2.5</a></li>
 <li><a class='version' href='/v2.1'>Version v2.1</a></li>