---+++ Repositioning HTML for CSS and javascript links

Modern HTML commonly uses CSS and Javascript. This requires <link>
elements in the HTML <head> element or <script> elements in the <body>.
Unfortunately this seriously harms re-using HTML DCG rules as components
as each of these components may rely on their own style sheets or
JavaScript code. We added a `mailing' system to reposition and collect
fragments of HTML. This is implemented by html_post//2 and
html_receive//1.

	* [[html_post//2]]
	* [[html_receive//1]]
