[det]reply_htmx(+HTML)
[det]reply_htmx(+HTML, 
+Request)Reply a plain HTML element as opposed to a complete HTML 
page as created using reply_html_page/2,3. 
While reply_htmx/1 is to be 
used in a normal HTTP handler (route), reply_htmx/2 
may be registered directly in the http_handler/3 
declaration to deal with simple cases where we do not need the Request 
data.