Need a way to specify type and allowable range for keywords

[scizen9]

This is a critical function from KTL. The daemon should respond to out-of-range requests with a standard error message (and not crash).

Other items we should consider for keywords:

1. short description text
2. long help text
3. format specification for printing (in show or gshow, or now lshow)

These are worth considering, but could also be optional. The type specification and out-of-range behaviour are more critical features.