Add capability of logging multiple emails

[backspace]

Hey, thanks for making this! I’m new to Elixir and Phoenix but enjoying building an application with TDD. I trigger two emails when a person creates an account in the application: one to the new person, and one to the administrator. So the current implementation where the JSON log file is replaced for each email prevents me from testing for both emails.

I realise this is a significant change and would break anyone’s application that relies on the current implementation. I could add another configuration flag to turn on this functionality? I figured I’d start with this possibility and seek your input. I had to add a step to delete the log file if it existed, which is a bit cumbersome.

Also, since I’m so new to the language, I am still learning the idioms; let me know if I’ve written anything in an awkward way.