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

[Dean Tribble]

>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