Mesh rescaling finished, line integration part 1.

doc/lua_api.md

include/gmsh_io.h

src/gmsh_io.cpp

src/maxwell_solver.cpp

tests/profile_differentiation_gpu.cpp

tests/test_basics.cpp

tests/test_differentiation.cpp

tests/test_differentiation_gpu.cpp

tests/test_lifting.cpp

tests/test_lifting_gpu.cpp

tests/test_mass.cpp