Builds a MIME type registry with common and custom types.

To create your own MIME type registry:

defmodule Mr.MIME do
  use MIME.Types, %{
    "application/vnd.api+json" => ["json-api"]
  }
end

This will build a registry of MIME types under mapping/0, and lists types/0 and extensions/0 for checking inclusion.

If you change the custom mapping passed into the macro, your module will need to be recompiled.