[TODO] Masks

[inxomnyaa]

Description:

See https://github.com/Brennian/Arceon/wiki/Masks

Masks basically are selection modifiers which change which blocks get iterated in (Async)Action::execute()

Might be useful for placing snow layers

They may also include noise algorythms

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TODO list:

• Figure out a syntax (probably add secondary parameter mask to //set, //replace etc)
• Implement masks globally (plugins + users can use it via API)
• Serialization
• Modify actions' outcome
• Mask extends CustomShape?