Implement dynamic page tree lookups.

No more caching a flattened page tree in doc->page_objs/refs.

No more flattening of page resources, rotation and boxes.

Smart page number lookup by following Parent links.

Naive implementation of insert and delet page that doesn't rebalance the trees.
Requires existing page tree to hook into, cannot be used to create a page tree
from scratch.
Hoist count skipping up to before we recurse.
Remove depth counter from page/resources lookups.

Instead of just relying on a depth count (which can easily be fooled
by poor but valid files) use mark/unmark based schemes for
pdf_lookup_inherited_page_item and pdf_lookup_page_number.
Fix pdf_count_pages_before_kid to cope with /Page with /Count in.
Prepare for multiple viewer application targets in makefile.
Add documentation files to make install target.
Silence a few warnings.
Throw exception on invalid page objects when looking up page numbers.

Also handle exceptions when parsing link destinations.
Set /Parent entry when inserting a page into the page tree.
Initial work on progressive loading

We are testing this using a new -p flag to mupdf that sets a bitrate at
which data will appear to arrive progressively as time goes on. For
example:

  mupdf -p 102400 pdf_reference17.pdf

Details of the scheme used here are presented in docs/progressive.txt
Import curl submodule.
Add mupdf-curl app

Windows and X11. Allows files to be fetched and displayed
as they are downloaded both with and without linearization, using
hints if available.
Bug 694431: Fix potential infinite loop.

Thanks to "willus" for pointing out this problem.
Collect together all code to do with appearance-stream creation
Update thirdparty/curl to include curl_config.h

This solves linux build problems.
Added newlines in error messages for X11 platform.
Add in missing files into winrt project from 15b9cdd84caf784abeb911ca7aaf1d317d201e88
Fix MIN/MAX confusion in edge list clipping.

The case with infinite scissor didn't work.
Bug 694429: Fix potential overflows in sprintf in pdfextract

Thanks to Pengsu Cheng for pointing out the problem.
Update CHANGES file with recent events.