added quick hull algorithm
added tests for quick_hull algorithm
added quick_hull in visualization
now some parameters are passed by reference, not by value
fixed bug in quick hull
added test for quick hull algorithm
changed std::iterator_traits<RanIter>::value_type to point_2 - our algorithm works with this type(Graham and Andrew work only with point_2 too). Some other small changes
Merge pull request #20 from Undin/quick_hull

Quick hull