Manual writing of extension modules

	SWIG needs some non-trivial tweaking to handle NumPy arrays (i.e., the use of SWIG is much more complicated for array arguments than running F2PY)
	We shall write a complete extension module by hand
	We will need documentation of the Python C API (from Python's electronic doc.) and the NumPy C API (from the NumPy book)
	Source code files in src/mixed/py/Grid2D/C/plain
	Warning: manual writing of extension modules is very much more complicated than using F2PY on Fortran or C code! You need to know C quite well...