Fix display of static pages

With recent versions of Pelican (I looked at 3.7.1), the theme didn't show
any static page anymore.  This is because the template variable changed
name from "PAGES" to "pages" at some point.

Fix archives page with Jinja>=2.9

use more standardized strftime formats

Fix handling of subscripts and superscripts (including footnotes).

Fix display of inline and block code

Add Google Analytics tracking code

Add styling for lists