modified parse_file() to read file, then call parse_content()
implemented content_list() node method
implemented delete_content() node method
implemented push_content() node method
fixed push_content()
implemented clone_list() node method
implemented preinsert() and postinsert()
implemented unshift_content() node method
implemented replace_with() node method
implemented detach() node method
fixed replace_with(), now creating new document for the replaced node
implemented disembowel() method
Merge pull request #7 from cafe01/master

implemented all methods needed by Web::Query::LibXML to work