operator: use non-RSI inducing operator function names.

* lib/std/operator.lua ([".."], ["[]"], ["{}"], ["#"], ["+"])
(["-"], ["*"], ["/"], ["%"], ["^"], ["=="], ["~="], ["<"], ["<="])
([">"], [">="]): Rename from these...
(concat, deref, cons, length, sum, diff, prod, quot, mod, pow, eq)
(neq, lt, lte, gt, gte): ...to these.
(['""']): Remove. Just pass the tostring function.
(["~"]): Remove. Just pass string.find.
Adjust all callers.
* NEWS: Update.

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