Configure cloning of data to happen on specific paths

[dumconstantin]

Currently, all producers will receive cloned data. This might be a speed issue when dealing with high-velocity data so, with proper measures of not modifying the references, producers can handle un-cloned data without tampering with the state.

As such, some paths should be excluded from cloning - or this should be an inclusion model instead:

createEngine({
  state: { ... },
  producers: [...],
  pathsToClone: [Path.items, Path.foo, Path.bam]
})

By not providing the pathsToClone property all data will be cloned.