Allow to specify root HTML node for RST formatter
Allow to specify root HTML node for RST formatter

It turns out that many RSS readers (or at least two I'm using:
http://feedly.com and http://twentyfivesquares.com/press/) do not handle
non-HTML tags in Atom content tag and skipping the whole content of
it. This patch allows to specify different (in this case <div>) node to
make readers happy.

FedericoCeratto/nimforum,FedericoCeratto/nimforum,nim-lang/nimforum,nim-lang/nimforum