Refactor as extension of Official Gem

[pboling]

asw-sdk-ruby-record is an official aws-supported gem: https://github.com/aws/aws-sdk-ruby-record

@bglusman said

wonder if we could/should refactor dynamoid to rely on that (official gem) for much of it's persistence/indexes logic etc since it's aws maintained and likely to be kept up to date, but that might be a larger project and is certainly a tangent from this question)

This is something we need to investigate and consider.