fixed detach() and replace_with() to keep node in the same document
fixed push_content() and unshift_content() to work on document node

because appendChild() is not supported on document node.
fixed detach(), improved replace_with()
Checking in changes prior to tagging of version 0.20.

Changelog diff is:

diff --git a/Changes b/Changes
index 9f40f79..dd69271 100644
--- a/Changes
+++ b/Changes
@@ -2,6 +2,12 @@ Revision history for Perl extension HTML::TreeBuilder::LibXML

 {{$NEXT}}

+0.20 2013-05-10T20:44:16Z
+
+    - improved replace_with() on document node.
+    - fixed push_content() and unshift_content() to work with document mode.
+    (cafe01)
+
 0.19 2013-05-10T01:03:58Z

     - fixed replace_with() and parent(),