Reworked _resolved_attrs() to allow columns to include hashes (with

Reworked _resolved_attrs() to allow columns to include hashes (with
as => select elements), and to add +columns (same syntax).
Current state:
  2 broken tests in CDBI emulation:-
    t/cdbi-t/max_min_value_of                      (Wstat: 512 Tests: 2 Failed: 2)
      Failed tests:  1-2
      Non-zero exit status: 2
Other tests work (suprisingly).
Documentation to be done.
Interaction between columns/select may be different....