Abstract classes/members

[Polanas]

Currently there is no way to express that a function has to be implemented by the child class.

I believe a way to declare abstract classes/members similar to how it's done in Java/C# would be beneficial.

Potential syntax:

---@class AbstractClass 
---@field abstract print: fun()
local class = {}

---Alternatively, declare an abstract function in a meta file
---@abstract
---@param sound string
class.produce_sound(sound)
end

---error: members of AbstractClass not implemented
---@class Child: AbstractClass