Provides a basic command module setup to reduce boilerplate

Example:

defmodule CommandedAggregateless.TestCommand do
  use CommandedAggregateless.Command,
    identifier: :id,
    prefix: "test",
    required_permission: "manage_tests"

  alias CommandedAggregateless.TestAggregateCreated

  inputs do
    field :id, binary()

    field :some_required_key, binary()
    field :error_in_handle, boolean()
  end

  validates(:some_required_key, string: true)

  aggregate do
    field :id, binary()

    apply_event TestAggregateCreated do
      %{aggregate | id: event.id}
    end
  end

  def handle(_aggregate, %__MODULE__{error_in_handle: true}),
    do: {:error, {:command_handler_error, "There was an error handling the command"}}

  def handle(%{id: nil}, command) do
    {:ok, %TestAggregateCreated{id: command.id}}
  end

  def handle(_aggregate, command) do
    {:error, {:aggregate_exists, "Aggregate #{command.id} already exists."}}
  end
end