Extend new_tag() to support content specification

[Chris Papademetrious]

In the Perl XML::Twig library, the new() element creation method at

https://www.xmltwig.org/xmltwig/twig_dev.html#METHODS_XML_Twig_Elt_new

supports three arguments:

* The tag name of the new element to create
* A hash of initial attribute values
* An array of initial content objects

The new_tag() method in Beautiful Soup supports initial attribute values but not initial content objects. This might be a straightforward extension of the UI, by allowing one or more string and/or Tag/BeautifulSoup objects to be specified after the tag name:

my_title = soup.new_tag('title', my_title_string_var)