* mln/io/abort.hh,
	* mln/io/fits/load.hh,
	* mln/io/pbm/load.hh,
	* mln/io/pbm/save.hh,
	* mln/io/pfm/load.hh,
	* mln/io/pfm/save.hh,
	* mln/io/pgm/load.hh,
	* mln/io/pgm/save.hh,
	* mln/io/pnm/load.hh,
	* mln/io/pnm/load_header.hh,
	* mln/io/pnm/max_component.hh,
	* mln/io/pnm/save.hh,
	* mln/io/pnm/save_header.hh,
	* mln/io/ppm/load.hh,
	* mln/io/ppm/save.hh,
	* tests/io/ppm/ppm.cc: Add documentation, review the code, put
          MLN_INCLUDE_ONLY gards, add missing function declaration (outside
          MLN_INCLUDE_ONLY).

git-svn-id: https://svn.lrde.epita.fr/svn/oln/trunk@1568 4aad255d-cdde-0310-9447-f3009e2ae8c0