Allow pdftoxml to accept options.
The version of pdftoxml on the old scraperwiki site accepted extra options
in the second argument.  This patch add the same argument to this version
of pdftoxml, to allow the -hidden flag to be added when needed.
Merge pull request #75 from petterreinholdtsen/pdftoxml-options

Allow pdftoxml to accept options.
Merge branch 'master' into pdftoxml-utf-8