I also added a test to make sure the time mesh is twice as
long as the frequency mesh. Obviously now some tests don't
pass... I will fix them in the next commit.
- little details : code cleaning, clang formatting, along
with documentation writing for c++ gf.
- separated the mesh in small class for better doc.
- work on documentation : reorganize specialisation, ...
- 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).
