message: Adding new `gmsh.[ch]pp` files to cmake
diff: set(SRCS
  element.cpp
  + gmsh.cpp
  hexahedron.cpp
  mesh.cpp
  mesh_operators.cpp
  @@ -29,6 +30,7 @@ set(SRCS
  set(HDRS
  element.hpp
  + gmsh.hpp
  hexahedron.hpp
  mesh.hpp
  mesh_headers.hpp
  