1.0.0  Feb 27 2007
 - Initial release.
 
2.0.0  Mar 07 2007
 - Removed BCrypt::Password#exactly_equals -- use BCrypt::Password#eql? instead.
 - Added BCrypt::Password#is_password?.
 - Refactored out BCrypt::Internals into more useful BCrypt::Engine.
 - Added validation of secrets -- nil is not healthy.