DRAFT : to be tested further...
- update gf<imfreq>
- write a specific mesh for matsubara frequencies
- now the cast series is :
mesh_pt --> matsubara_freq --> complex<double>
- matsubara_freq is just the matsubara frequency
- arithmetic of the mesh_pt casted to matsubara_freq
- arithmetic of matsubara_freq is casted to complex, except + and -,
which are kept as matsubara_freq.
- evaluator now accept : int, mesh_pt, and matsubara_freq
for matsubara_freq : for negative omega, use conjugation
for omega outside windows, evaluate the tail on omega.
- as a result : g( om - nu) where om, nu are 2 meshes points,
is the extrapolation outside the grid if necessary.
- updated tests
- added evaluation for tail.
