simplify_obc.cc uses the single-site algorithm when Dmax == 0.
Fixed the signature of simplify_obc() for many tensors.
ArnoldiSolver now uses simplify_obc()
set_canonical_2_sites() now allows not using set_canonical() on the following site, which saves times when this site is going to be updated.
simplify_obc() now calls set_canonical_2_sites() with the optimization flag to avoid using set_canonical() on the site that is overriden.
Fixed typo in set_canonical_2_sites_inner()
simplify_obc() now returns the norm of the state.
Simplified ArnoldiSolver so that it calls norm2/scprod less times.