update to ashikawa-core 0.7.2

Hello there,
this is my attempt to make ashikawa-ar talk to ashikawa-base 0.7.2

Please note that I focused on major api changes from 0.3 to 0.7.x and make tests passing, for sure there is more work to do, in particular I've made some assumptions on usage of key and id and I'm not completely sure if I'm right, also we've to wait for a new version of  Virtus as current version is causing a lot of issues, Solnic says [ it will came in may](https://github.com/solnic/virtus/issues/160).

Hope it helps