List of features to be implemented (not in any particular order)
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- xoj2pdf on command line
- load images as bg if given on command-line (as with PDF on commandline)
- load PDF pages only on demand (create empty pixmaps at first if can
   parse PDF geometry ourselves, else try pdfinfo ??)
- de-map space key from button bar
- lasso selection tool
- flatten (incl undo/redo...) - enabled only if nlayers>1
- resize selection
- text tool, font chooser, default font
- color chooser (papercolor, pen color); maybe more default colors
- printing: print-options, save printer settings (throughout a session,
   and on disk) (maybe a separate config file .xournal/gnome-print-settings)
- help index
- pressure sensitivity
- insert images (screen capture or from file or from clipboard), 
  not as full-page backgrounds (new ITEM type)
- more pen/highlighter shapes (chisel)
- convert to/from Jarnal format; to/from MS Journal format???
- recalibration upon screen resize / compensation for miscalibration
- find a better behavior for vertical space tool across page boundaries ?
- key mappings (pgup/dn for full page, up/dn for scroll)
- copy/paste of an entire page (beware if PDF bg is not compatible!)
- simple drawing tools: rectangles, ellipses
- option to save all annotated files within the .xoj
- non-antialiased version for handhelds
- customize autogenerated save file names