Various improvements to perfect foresight homotopy

– new option “endval_steady” to pf_setup command to recompute terminal
  steady state in the homotopy loop

– new options “homotopy_linearization_fallback” and
  “homotopy_marginal_linearization_fallback” to pf_solver and pfwee_solver
  commands, to get an approximate solution when homotopy fails to go to 100%

– new options “homotopy_initial_step_size”, “homotopy_min_step_size”,
  “homotopy_step_size_increase_success_count” and “homotopy_max_completion_share”
  to pf_solver and pfwee_solver commands to fine tune the homotopy behaviour

– removed option “homotopy_alt_starting_point” to pf_solver command, not really
  useful

– new options “steady_solve_algo”, “steady_tolf”, “steady_tolx”,
  “steady_maxit”, “steady_markowitz” to pf_solver and pfwee_solver commands, to
  control the computation of the terminal steady state (and remove the
  equivalent options which previously had different names in pfwee_solver command)