Support multiple event stores

[slashdotdash]

Allow multiple event stores to be used in an application by providing an EventStore macro to use in your own module, as per Ecto's repo.

Define your event store module:

defmodule MyApp.EventStore do
  use EventStore, 
    otp_app: :my_app

  # Optional `init/1` function to modify config at runtime.
  def init(config) do
    {:ok, config}
  end
end

Configure the event store:

config :my_app, MyApp.EventStore,
  serializer: EventStore.TermSerializer,
  username: "postgres",
  password: "postgres",
  database: "eventstore_dev",
  hostname: "localhost",
  pool_size: 10,
  pool_overflow: 5

config :my_app, event_stores: [MyApp.EventStore]

Usage:

:ok = MyApp.EventStore.append_to_stream(stream_uuid, expected_version, events)

[hauleth]

This would provide additional pro: there could be init callback like in Ecto that would allow to load configuration in runtime instead of relying on some weird tooling.

[slashdotdash]

Work in progress on branch feature/multi-event-store.

[slashdotdash]

Done in #168.