modified driver lanc_lda1b to read Bethe hamiltonian
BUG fixed in lanced_lda1b:
calculation of total density was biased by small value of Ltau.
At T=0 one needs a large number of tau points. This is fixed
by a function calculating the density using NL points (the best
approximation you can have).
hint:A more solid implementation would be to code the non-linear FFT.
code moved to Nup,Ndw basis rather than Ntot,Sz.
This is the first step towards performance boost with integration of
look-up tables and Hilbert space splitting strategies.
Merging with 'devel' branch.
Code moved to nup,ndw basis.
Ready to merge with multi-band code as soon as it
is thoroughly tested.