Crate factorial

Compute the factorial

This crate provides some convenient and safe methods to compute the factorial and related functions in O(n) time.

They are not necessarily the fastest versions: there are prime sieve methods that compute the factorial in O(n (log n loglog n)^2). Patches are welcome.

Traits

DoubleFactorial	Unary operator for computing the double factorial of a number
Factorial	Unary operator for computing the factorial of a number