[cairo] PDF backend starts to get interesting

[chris nuernberger]

In order to use Cairo for my app, I would need the encryption stuff,
and also some control over the pdf table of contents and section
thumbnails.  I don't use cairo now for my application, but I would
really like to, however absolutely the next set of features I am
adding is support for TOC and document navigation stuff.

I really don't think all this makes sense to put in cairo.  The mixed
color space stuff, and moving away from 8 bit RGB in everything is
definitely necessary, but really I think that a really full-featured
PDF library that works well with cairo is more appropriate (as Carl
mentioned).

In that vein, the cleanest PDF library I have ever come across (and
used a bit) is haru.  It is far from containing all the features we
talk about, but it is super clean and very close to the file format,
i.e. a pretty darn light wrapper.  Not a lot of code, so I have found
it really easy to work with.

Chris