[E-Lang] Deprecation (was Immutable map operations)

[Marc Stiegler]

> >Assuming that's a yes and that you go with the current syntax proposal
> >for collections, I think it should be a long term goal to replace
> >String+ with String|. To that end, I think String+ should be marked as
> >deprecated right out of the gate. String+ should also be implemented
> >as expanding to String|.
>
> Great idea!  I'm not entirely sure what being deprecated means
> operationally within an interpreted language, but here are some options:
>
> - well documented in the description of the function (including the
> preferred alternative)
> - well documented in the list of deprecated functions
> - traced, with a mode to report it
> - the use of each deprecated feature is reported only once per run of E

It also means that it is described as "deprecated" in Walnut, which gives
the user a slightly greater incentive to learn the alternative sooner rather
than later :-)

--marcs