union fix

CMakeLists.txt

include/constants.h

include/intersections.h

include/split_triangle.h

include/triangle.h

src/shapes/triangle.cpp

src/union.cpp

src/utilities/contourize.cpp

src/utilities/intersections.cpp

src/utilities/orientation.cpp

src/utilities/split_triangle.cpp

tests/union_tests.cpp

tests/unit_tests/contourize_tests.cpp

tests/unit_tests/orientation_tests.cpp

tests/unit_tests/split_triangle_tests.cpp