Allow JSON/YAML/some sort of standardized formatting for entry files

[ApprenticeofEnder]

This might involve creating a PasswordData struct, along with some provisions to retrofit existing password entries, but having the entries be in encrypted JSON or YAML would allow for slightly easier development in terms of working with the files and expanding the scope of potential data contained within.

[alexanderkjall]

Maybe this should be a configuration option, it would make it hard to inter-op with the other pass implementations, but would make it easier to expand functionality.