Updated to a more cryptographically-secure salt generator.
Checking to see if the OpenSSL function exists, and if not, using less-secure salt-generation.
Added warning when OpenSSL is not installed.
Merge pull request #7 from WDC/more-secure-salt

More Cryptographically-Secure Salt Generator.

Will fall back to mt_rand based salt generator and give a warning if OpenSSL is not installed