Fixing numerics for Finite Differences

src/Equations/eq_1_ag_unit_test.hpp

src/Equations/eq_2_ag_unit_test.hpp

src/Equations/eq_base_unit_test.hpp

src/Equations/eq_unit_tests.hpp

src/FiniteDifference/Average.hpp

src/FiniteDifference/Derivative.hpp

src/FiniteDifference/FDScheme.hpp

src/FiniteDifference/FDScheme_unit_tests.hpp

src/FiniteDifference/eq_unit_test.hpp

src/Matrix/Matrix.hpp

src/util/util_num.hpp

src/util/util_num_unit_tests.hpp