Merge pull request #9 from mborne/master

offset tests & round
[CMAKE]add doxygen support to build the documentation (make doc)
round Kernel::FT values to smaller rationnal ( round(1.68965,10) => 17/10 )
allows 3D translation of 2D geometries
SFCGAL::io::OsgFactory (available only with the optional OSG support)
SFCGAL::io::OsgFactory (available only with the optional OSG support)
add helper to save a geometry in a file
cmake, default no OSG
remove include/SFCGAL/config.h (generated by cmake)
cmake and co
floor/ceil/round rationals (embryo, need completion and tests)