Add atom or RSS feed icon to navbar.

Right now this is only active on the index page. That's because intuitively one would expect a feed on a category page to be specific for the category. It's not clear to me, however, how one can test whether the page is a category page.
Adds published day to article info on index.

Also moves the comment count to the same (“footer”) line.
Allows a page's menu label be different from its title.

The title of a page by default is used both for printing the title of the
page's content, and, if pages in menu is enabled, for providing the label
of the menu item. Sometime one may want those to be different, though, such
as having a short (e.g., single word) menu item label, and a longer page title.
This change allows that by adding a Menulabel metadata attribute to the page's
header (Menulabel: in markdown, :Menulabel: in rst).
Allows feed icon to appear on pages and posts as well.
Adds category for each article on front index page.
Adds configurable spacing around separator dot.