Sends email using Customer.io's API.

Use this adapter to send emails through Customer.io's API. Requires that an API key was set in the config.

Example config

# In config/config.exs, or config.prod.exs, etc.
config :my_app, MyApp.Mailer,
  adapter: Bamboo.CustomerIOAdapter,
  api_key: "my_api_key"

# Define a Mailer. Maybe in lib/my_app/mailer.ex
defmodule MyApp.Mailer do
  use Bamboo.Mailer, otp_app: :my_app
end