added: lanczos_arpack.f90
some updates:

+ updated ED_SOLVER with the latest version of the SERIAL code git:2484b50f84b467797528 .
+ some changes in the ED impurity solver for lattices: bath array now REQUIRES Nlat index to
be the first entry (bath(Nlat,Nb(1),Nb(2))).
+ minor changes from sc+disorder tests.

perhaps other even minor changes.