[BREAKING] Refactored Skinny ORM, added NonRelationalMapper 

### Changes

 - SkinnyNonRelationalMapper is newly added
 - SkinnyTable is deprecated, SkinnyRelationalMapper is preferred
 - SkinnyJoinTableWithId has been removed
 - Much refactored duplicated implementations internally

This is published as 1.0.14-SNAPSHOT to sonatype snapshots repos. 

All the unit tests already passed. Just to be safe, I'll check my projects with this version before merging this PR.