[poppler] Merging the better_object branch for Poppler 0.58

[Albert Astals Cid]

This wednesday i'll release Poppler 0.56 (if all goes according to plan).

Then around 20 July (may get delayed since that day starts the KDE yearly 
conference) i'll release Poppler 0.57.

My plan is just after doing the 0.57 release merging the better_object branch 
to master so it gets released with Poppler 0.28 around 20 August.

I'm almost convinced there will be some regression since the code diff is 
*huge*, but i'm also convinced it gives us a much nicer API to work with, in 
particular for "non hardcore contributors", see the missing free() in the 
patch at https://bugs.freedesktop.org/show_bug.cgi?id=99271 so in the long run 
we end up winning.

This means you have two months since now until a version with the 
better_object code gets released, please review the branch as soon as 
possible.

Cheers,
  Albert