Adding generic types.

src/FiniteDifference/Upwind_gradient.hpp

src/level_set/redistancing_Sussman/HelpFunctionsForGrid.hpp

src/level_set/redistancing_Sussman/RedistancingSussman.hpp

...level_set/redistancing_Sussman/tests/convergence_test.cpp

...istancing_Sussman/tests/redistancingSussman_unit_test.cpp