list: export all apis for automatic argument type checking.

* specs/list_spec.yaml: Specify argument checking of all apis.
* lib/std/functional.lua (map): Move core function from here...
* lib/std/base/functional.lua (map): ...to here.
* lib/std/list.lua (project, map, map_with, transpose): Use it.
(m): Collect exported object methods here.
(List.__index): Set to m.

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