refactored agrad/matrix.hpp. moved the classes around to a more natural order
refactored agrad/matrix.hpp. moved the classes around to a more natural order

stan-dev/stan,stan-dev/stan,stan-dev/math,stan-dev/stan,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/stan,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/stan,stan-dev/math