Change in doc_document.c to account for oxps type.  Also error catching when file fails to open.

Removal of null checks for object freeing in interface to mupdf.
Rework the xref loading code in preparation for separately holding sections

Now directly read the sections handling trailers as we go, rather than
processing the most-recent trailer up front. Handle XRefStm separately
from the main section-loading loop so as to ignore Prev when it occurs
in a XRefStm (as specified in the spec).  That has the side-effect of
avoiding recursion.
Maintain the separation of xref sections when loading a document

Also on first alteration create a further section to hold the updates. This
is in preparation for supporting incemental update.
Fix XPS leaking fz_buffers for images.

fz_new_image_from_buffer was building a new buffer from the data in
the supplied buffer, rather than just using the supplied buffer. Also
move the code into line with our standards; don't pass ownership of
the buffer.
Remove debug prints from the file spec parsing code
Fix up of winrt project so that all the configs and platforms compile
Fix for crash if no file present and links button pressed.
Update openjpeg submodule with ARM build fix.
Add ctags make target.
Silence warning.
Simple PCL output

Mono only for now. Copy the appropriate fz_pcl_options for the printer required
and pass that to fz_write_pcl_bitmap.

Add pcl output to mudraw - .pcl produces laserjet 4 compatible pcl.
fix two issues in new pdf_xref code

* at one place, code returns from inside an fz_try which borks up the error stack
* pdf_load_xref wrongly assumes that at least one non-empty xref has been read if there were no errors thrown during parsing
prevent double-free

the object referred to by the variable obj in pdf_repair_xref is always dropped on error, even if it it never kept a reference. Nulling it out after use prevents that.