Definite primality verdict for small numbers

[fjarri]

For small enough numbers (e.g. u64) we can have a definite verdict in the same time it takes to run the general BPSW probabilistic test. This may be a sequence of Miller-Rabin tests with predefined bases, or perhaps the Lucas-V test, given how few false positives it has, and the fact that it can be sped up (see #2).