Implement nextPermutation for bidirectional ranges.
Implement nextEvenPermutation.
Improve ddocs for nextPermutation and nextEvenPermutation.
Improve documentation.
Add unittests for non-default sorting order.
Fix rollover bug in nextEvenPermutation.
Add non-trivial example for nextEvenPermutation.
Oops, fix typo in ddoc.
Merge pull request #1022 from quickfur/permute

Implement nextPermutation and nextEvenPermutation