Merge KeyAware into MapperAware #5
Description
When Mapper delegates to a strategy it places the burden on that strategy to propagate the key, which it does by invoking Mapper again with the key it received. If a strategy implements MapperAware but not KeyAware it will drop the key information, which is never desirable. Therefore, any strategy electing to be MapperAware should also accept the burden of being KeyAware, assuming we want to continue passing keys around in this fashion.
The reason they have been created as separate interfaces at this time is just to avoid breaking compatibility for code that currently implements MapperAware. In the next major version we should seek to either merge both interfaces into one or find a better way to propagate keys through the mapper altogether.