update-template: remove empty meta description tags
Work around lxml / PyQuery bugs with unicode

If you have HTML which isn't parseable as XML – i.e. HTML5 – PyQuery
will use lxml.html.fromstring() to parse it, which treats all input
as latin-1(!) even if it arrived in a Python 3 unicode string.

The solution is to parse the HTML string using lxml.html.fromstring
with a declared Unicode parser and then pass the result to PyQuery
as elements. See https://github.com/gawel/pyquery/issues/31 and https://bugs.launchpad.net/lxml/+bug/898072

This also required working around a separate bug handling lxml
_ElementUnicodeResult objects: https://github.com/gawel/pyquery/issues/32
Correct handling of time/meta microdata

This allows using both <time> and <meta> tags to serve as the
schema.org dateCreated/dateModified/datePublished properties