1st draft of complete class-based std.random successor

[bearophile]

Joseph Rushton Wakeling:

> How does your desired concept relate to the existing 
> std.algorithm.nextPermutation ... ?

The API of the lazy permutations/combinations ranges is similar 
to the one I have written here:
http://rosettacode.org/wiki/Permutations#Fast_Lazy_Version

That is also very similar to the permutations/combinations here 
(with the "r" optional argument):
http://docs.python.org/2/library/itertools.html


To the one in Phobos is used like:

auto items = [1, 2, 3];
do
     writeln(items);
while (items.nextPermutation());


The permutations/combinations range is used like (the boolean 
template argument is to specify if it has to copy the buffer or 
not):

[1, 2, 3].permutations!false.writeln;

Bye,
bearophile