Document all tuplet-related changes

[ciacob]

Document all tuplet-related changes, i.e., include the changed behavior in the documentation, e.g.:

Nudging a tuplet's (A) Cluster over a regular Cluster, or over the first Cluster of another, adjacent tuplet (B), nudges instead the first tuplet (A) entirely. This is to support the scenario where a Voice content is entirely made out from tuplets, and rearranging content via the "nudge" function would be quite difficult.