Modified tests following addition of indices.
Force g_tau to have 1/iw tail to ensure FTs are correct.
Modified tests following change to tails.
API change: G_tau_view -> G_tau, G_tau -> _G_tau, etc.
Added doc comments to ctqmc.hpp for automatic generation.
Put Hilbert space tools into triqs::utility namespace. Hopefully it will
not cause too much havoc.
Improvements of imperative_operator

* Templated on ScalarType (type of matrix elements).
* imperative_operator::operator() may pass a number of extra arguments
to ScalarType::operator() when applied to a state. This feature is
useful with user-defined function-like scalar types.
* New method update_coeffs(Lambda L) applies functor L to all
coefficients.
Merge branch 'hilbert_space_tools' of github.com:TRIQS/cthyb into hilbert_space_tools