Need C Algorithm

[Doug Gwyn <gwyn>]

There is a permutation generator in the Collected Algorithms of ACM
(long ago, so probably in the bound Vol. 1).

You can also design a permutation generator by recursive application
of the rule:
	Perm( N ) = { N-inserted-at-each-position-in-Perm( n-1 ) }
This makes a pleasant programming exercise.