Rewrote generatePassword to address biasing flaw.

Added biasing test as recommended in https://groups.google.com/d/msg/golang-nuts/IzeoO9p9w1g/HfDdfNicGCUJ

Added generatePassword2 to compare my implementation to using crypto/rand.Int. Testing indicates that my implementation is about 9-10x faster, and is much less wasteful.
Merge branch 'master' of https://github.com/JustinJudd/passgen