Macro template instantiations

[adamdempsey90]

Something like:

  #define ARTEMIS_FOR_ALL_GEOMS(M) \
    M(Coordinates::cartesian)      \
    M(Coordinates::cylindrical)    \
    M(Coordinates::spherical1D)    \
    M(Coordinates::spherical2D)    \
    M(Coordinates::spherical3D)    \
    M(Coordinates::axisymmetric)

and then,

  #define INSTANTIATE_ESTIMATE(G) \
    template Real EstimateTimestepMesh<G>(MeshData<Real> *md);

  ARTEMIS_FOR_ALL_GEOMS(INSTANTIATE_ESTIMATE)

  #undef INSTANTIATE_ESTIMATE