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* add include_rst() and include_mkdn() as functions available in Jinja templates
* css and js from included templates is now always included, regardless of where
in the child template the include method is called.
* add "content" template filter which will merge css/js from the given content
object into the parent template
* add link_css_url(), source_js_url() and complimentary head_link_tags() and
head_script_tags() template functions to be able to include CSS/JS URLs from
any template.
* make HTTP request method handling more robust. Its now easier to respond to
request methods that are not GET/POST and we will now correctly return a 405
Method Not Allowed response when the view can not handle the request method
sent over.