gravity → core Relation

File in include/vulcan/gravity	Includes file in include/vulcan/core
GravityTypes.hpp	VulcanTypes.hpp
J2.hpp	Constants.hpp
J2.hpp	VulcanTypes.hpp
J2J4.hpp	Constants.hpp
J2J4.hpp	VulcanTypes.hpp
PointMass.hpp	Constants.hpp
PointMass.hpp	VulcanTypes.hpp
SphericalHarmonics.hpp	Constants.hpp
SphericalHarmonics.hpp	VulcanTypes.hpp