Obfuscate password

Obfuscate passwords using base64 encoding w/ hashes for verification (and plaintext backwards compatibility!)

Obviously this is *not* a good way to protect passwords; it's only intended prevent others from casually observing your plaintext password on the filesystem. No such assumptions of security should be made, especially concerning individuals that may be fluent in base64.

Initial support for the Socialcast password -- other keys could be added.
Use named subjects, like such:

`subject(:clarify_credential_hash) { Socialcast::CommandLine.send(:clarify_credential_hash, opaque_credentials) }`

then use it like

`clarify_credential_hash[:password].should == clear_credentials[:password]`