Added accessor positive only to MeshImFreq
Added linear_to_index to matsub_freq
Fixed abs bug in bravais_lattice + added method

When constructing the last unit vector in 2D, the sanity check was wrong because of usage of abs instead of std::abs.

Added method energy_on_bz_path_2 that returns the energy *matrix* at each k point on a given path instead of the eigenvalues of this matrix. The name of the function should be changed (to energy_matrix_on_bz_path?)

Renaming energies_on_bz_path_2 to energy_matrix_on_bz_path
Small fix in gf doc.
test of mc_tools with complex added, bug in statistics corrected

Signed-off-by: tayral <thomas.ayral@cpht.polytechnique.fr>
Merge remote-tracking branch 'triqs_lib/master' into HEAD
Merge branch 'fix_jackknife' into HEAD