Add a third optional argument to specify the SecureRandom method to call

Some passwords may not accept the character set generated by the
default method so we'll provide access to all the methods provided by
SecureRandom. Obviously some of these are poor choices for passwords,
but we'll provide the flexibility to use all of them.
Add base64 and some length specific tests
Fix rubocop and address issues it found
Remove unit tests that call Base64::strict_decode64
Merge pull request #2 from sdodson/base64

Base64 or URL encoded secrets