refactor: move unshared methods out of std.base.

* lib/std/base.lua (merge): Move from here...
* lib/std/table.lua (merge): ...to here.
* lib/std/base.lua (append, compare, concat): Move from here...
* lib/std/list.lua (append, compare, concat): ...to here.
* specs/object_spec.yaml (std.object): Adjust.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>