Implement built-in CRDTs: LWW Register

[guiltygyoza]

Background

Register types are useful for CRO to specify a single value that can be updated concurrently by multiple nodes. LWW (Last-Write-Win) Register is a basic type for this purpose.

Task

• implement
• test
• document how this type works and its usage

Resources

• https://lars.hupel.info/topics/crdt/07-deletion/
• https://jsonjoy.com/specs/json-crdt/model-document/crdt-algorithms see the section on "Last-Write-Wins (LWW) CRDT Algorithm"
• https://www.bartoszsypytkowski.com/operation-based-crdts-registers-and-sets/

[joaopereira12]

I got this.