Deep projections (:only, :except) are unaware of nesting

[marshall-lee]

Failing example:

context 'with nested attributes' do
  before do
    subject.expose :additional do
      subject.expose :something
    end
  end

  it 'preserves nesting' do
    expect(subject.represent({ something: 123 }, only: [ { additional: [ :something ] } ], serializable: true)).to eq(
      additional: {
        something: 123
      }
    )
  end
end

Deep projections work well when passing to presenter exposures (:using options) but they should work with nested exposures too.

Will be fixed in #151