Alistair Boyle

spice_eit: fixed unit test (dead call to csolve --> spice_eit)

inv_solve_core: fixed bug where img0 background not stripped when doing difference imaging, just before returning results

fixed inv_solve_core test

gmsh_write_mesh: write GMSH v4.1 .msh mesh files from an image, fwd_model or inv_model including elem_data

gmsh_read_mesh: comprehensive testing of gmsh v2.2, v4.0, v4.1 in 2D and 3D

gmsh_read_mesh: refactor original v2.2, v4.0 test meshes into seperate files like the other test files

gmsh_mk_fwd_model: comprehensive testing of gmsh v2.2, v4.0, v4.1 in 2D and 3D; fixes for parsing out electrodes in v2.2 format

gmsh_read_mesh: learned v4.1 format and fixes for unreliable v4.0