Add l3htoks: typeset and get the result as a token list

The \htoks_set:Nn <tl> {<tokens>} command goes through
the <tokens>, expanding expandable tokens, performing
(most) assignments, and when it finds characters, or a
few other TeX primitives, it stores them into the <tl>.
Of course, \htoks_set:Nn 's parser does not know all of
TeX's primitives.  If an unknown primitive is needed,
just include it as \htoks_code:n {<code>}, which stops
the parser and resumes it after the <code> is performed.
Thanks to \htoks_code:n, one can adapt many LaTeXe
commands to work as expected within \htoks_set:Nn.  For
instance, \textbf, \Large, \mbox, \pageref, \label work.


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@4430 de43f980-851b-0410-b2f7-c40aca1f87e0