Add emacs-creds recipe

- A brief summary of what the package does.

Sometimes, we need to parse more information than just credentials in the ~/.authinfo(.gpg) file.
Provide some basic functions to do just that.

- A direct link to the package repository.

https://github.com/ardumont/emacs-creds

- Your association with the package (e.g., are you the maintainer? have you contributed? do you just like the package a lot?).

I'm the maintainer.

- Test local to package ok

- Test local to install the resulting package ok

Cheers,