adding tools to robustly compute the orientation of three given points
benchmark completed
cleaning + example + documentation page
 cleaning doc and concepts
an adapter to orientation functor in order to have a customizable predicate
2d to 2D
renamming 2D into 2, the number gives the number of points required minus one
 radius functor added for alpha-shapes
 renamming (orientation = general, halfPlane in the linear case), general concept of orientation functor and documentation updated
merging with master
edits in doxygen comments
small doc edits
small doc edit
 doc issues
merge with master
Merge pull request #775 from troussil/DeterminantTools

New tools to robustly compute geometric predicates