Key is received as param in many functions

[luispeerez]

Hi, I have noticed that the key (API key) is required in this function make_request_with_key https://github.com/grvty-labs/ex_openpay/blob/master/lib/openpay.ex#L113

I have made a fork with a change that involves to send the API key via authorization headers encoded in Base64,

https://github.com/spaceship-labs/ex_openpay/blob/master/lib/openpay.ex#L93

it works, so I wanted to know if the main idea of the api was to send any API key when calling a function or to always use the one that is set in the config application or the system environment

Application.get_env(:ex_openpay, :api_key, System.get_env "OPENPAY_API_KEY")