Application restart introduced.

When processing a restart request, the router sends a QUIT message to all
existing processes of the application.  Then, a new shared application port is
created to ensure that new requests won't be handled by the old processes of
the application.

docs/changes.xml

@@ -43,6 +43,12 @@ process and thread lifecycle hooks in Ruby.
 </para>
 </change>
 
+<change type="feature">
+<para>
+application restart control.
+</para>
+</change>
+
 <change type="bugfix">
 <para>
 TLS connection was rejected for configuration with more than one