ISSUE-65 Added new NonceGenerator static class with a ThreadSafeNonce
Have also added tests using Parallel.For to show concurrent runs giving unique nonces, and an Explicit test to show how the old method could produce duplicate nonces.
Changed RNGCryptoServiceProvider to be a static singleton
Merge pull request #66 from gregsochanik/nonce-watch

Added new NonceGenerator static class with a ThreadSafeNonce