Today's programming challenge - How's your Range-Fu ?

[Walter Bright via Digitalmars-d]

Challenge level - Moderately easy

Consider the function std.string.wrap:

   http://dlang.org/phobos/std_string.html#.wrap

It takes a string as input, and returns a GC allocated string that is 
word-wrapped. It needs to be enhanced to:

1. Accept a ForwardRange as input.
2. Return a lazy ForwardRange that delivers the characters of the wrapped result 
one by one on demand.
3. Not allocate any memory.
4. The element encoding type of the returned range must be the same as the 
element encoding type of the input.