Improve performance of is_prime() #6

We can speed up is_prime() for numbers which contain small factors (<=53) by using
the very fast GCD routine from GMP before bringing out the big guns.

Thanks to @danaj for the suggestion.
Fix large prime test
Add benchmarks comparing each Math::Primality function to Math::Prime::Util
Update version in Build.PL
Add simple bigint test case
Add change summaries for 0.06 - 0.08
Speedup for is_prime using two 32-bit GCDs (trial division for primes <= 53)
Adjust benchmarks
Documentation updates
Fix AKS
AKS is fast to 347
Remove duplicated code introduced by a merge
Merge changes from upstream
Change to v6 AKS