Improve GOMpy and LUA binding

[BrunoLevy]

• try to get rid of strings everywhere, starting from command-state that could use typed representation instead
• gom slots that take Any and ArgList as arguments
• NL::Vector improvements:
  • make NL::Vector closer to numpy arrays
  • support for non-contiguous arrays in NL::Vector
  • array protocol ? buffer protocol ?
• equality and inequality tests for GOM object wrappers
• make metaclass wrapper inherit python object so that issubclass works with GOM objects
• xxx = XXX(args) instead of xxx = XXX.create(args) (done in Python, not yet in Lua)
• JAX interop
• split python_interpreter.cpp, separate vec/mat interop
• iterators
• make gom interpreter inherit python module so that we can import gom.xxx from gom (in fact did it differently, by overriding gompy's __getattr__ and declaring sub-stuff that i wanted to make inportable in global module table)
• a GOM mechanism for graphic object attributes, or set_color, set_mesh_color, set_mesh_width etc... slots in shader
  • How it works now: there is no special mechanism, uses conversions from string and to string.
  • What we would like it to do:
    • write:
      mesh.shader.mesh_style.width = 5
mesh.shader.mesh_style = '0.5 0.5 0.5 1.0;5' --backward compat
      mesh.shader.mesh_style = { {0.5,0.5,0.5,1.0}, 5 } --from table Not yet, we shall see later...
    • read:
      x = mesh.shader.mesh_style.width
print(mesh.shader.mesh_style)
    • implement MetaBuiltinStruct and MetaStruct
    • register meta information for PointStyle, MeshStyle, SurfaceStyle, ColormapStyle
    • implement generic serializer
    • implement StructPropertyRef

[BrunoLevy]

Explanation about how to implement Python iterators in the C API.