tuned

Renamed attribute dlo into attribute ferrack

Added quantifier elimination in dense linear orders after Langford; locale dense_linear_order renamed to constr_dense_linear_order (since it requires the beween constant). locale dense_linear_order is now the classical definition of DLO. constr_dense_linear_order is an instance of dense_linear_order; Method dlo now applies the langford QE, odl Method dlo renamed to ferrack, since it ia a QE only in interpretations where between is interpreted in a manner to vanish after substitution.

Tunes Proof

begin_theory: simplified interface, keep thy info empty until end_theory;

clarified init/begin_theory: no longer depend on thy_info.ML; tuned;