apply returns applied events

[paneq]

that makes testing much easier when commands are used to build state.
Developers can easily opt-out by doing

def apply(*events)
  super
  nil
end

in their class.

or by explicitly returning nil or self

  def supply(quantity)
    raise NotRegistered unless @store_id
    apply(ProductSupplied.new(data: {
      store_id: @store_id,
      sku: @sku,
      quantity: quantity,
    }))
    nil
  end

[paneq]

Related to #109

[mostlyobvious]

Seems like a step in good direction without causing much trouble.

[mlomnicki]

I think apply should be private although that's a separate issue.

Overall this idea is an improvement to what we have currently so +1

[andrzejkrzywda]

A good change. Should the README/release_notes change be part of the PR, given that we change the public API?

[paneq]

@andrzejkrzywda yep! Will do when we release.