- change the underlying data : do not flatten the linear indices of the
mesh into a single index, keep a higher dim array.
- easier for various places, and necessary for g(nu,nu').
- work on several 2 part. containers.
- add default target (may not be always matrix_valued)
- correct previous commit (for scalar gf, the new check was not compiling)
- correct windowing of linear mesh (left point corrected as right point for rounding error
- lazy_fourier and co --> fourier
- ex fourier --> make_gf_from_fourier to make a new gf
- = fourier (g) works only iif lhs is a view, like scalar.
- updated python (commented fourier method).
