[WIP] Upgrade to Elixir 0.14.x

This is a WIP of making Dynamo work with Elixir 0.14.x

There are still 9 specs failing, I'm publishing it because I'm kinda stuck so if anyone is willing to help that would be awesome.

I'm not 100% happy with the way I integrated maps but my goal was to get the specs passing and then gather feedback and see how we can improve that.