Allow link/meta in body; treat like img/br

In HTML5+RDFa, link/meta tags are allowed anywhere in the document body. They
are treated as (void) flow content, i.e. they are empty and do not break flow.
Before, the LinearDoc code did not allow link/meta inside inline tags, causing
exceptions to be raised when processing many articles, such as
http://en.wikipedia.org/w/index.php?title=Nikolai_Lobachevsky&oldid=612652482

See http://www.w3.org/TR/rdfa-in-html/#extensions-to-the-html5-syntax for
further details.

LinearDoc.js
* Treat link/meta as void flow content, like image/br .

tests/*
* Fix tests (because the change trivially alters the dumped header output)
* Add new tests for link/meta in body (block + inline context)

Change-Id: Ic8019ca9f9c184a891df6c3c29854554f0934d38