Add value to move and copy operations

[upsidedownsmile]

At the moment it is not possible to get which value was moved or copied when computing a diff because the paths need to be computed step by step.

This pull-request adds the value to those operations when they are computed, which allows to get the value directly from a move/copy change.

Solves #134

[LouizFC]

It is better to make this feature behind a optional flag. This could cause serious problems in bigger payloads