refactor: factor functional.op into new std.operator module.

* lib/std/functional.lua (op): Move from here...
* lib/std/operator.lua (M): ...to here.
(M[".."], M["{}"], M[#"], M["~"], M["%"], M["^"]): New operators.
* local.mk (dist_luastd_DATA): Add lib/std/operator.lua.
* build-aux/config.ld.in (files): Likewise.
* local.mk (dist_module_DATA): Add std.operator.html.
* NEWS: Update.

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