Operator overload

[JonathanOrr]

This pull request aims to add operator-overloading to the classes created by the original library

The usage example of the added feature is as follows:

require"class"Vector2=Class:extend()
functionVector2:init(x, y)
self.x=xself.y=yend-- attributes --Vector2:set{x=0, y=0}
-- operator overloading --functionVector2:__add(other)
returnVector2(
self.x+other.x,
self.y+other.y
)
endfunctionVector2:__tostring()
returnstring.format("Vector2(%f, %f)", self.x, self.y)
end-----------------------------------------------------------localvec1=Vector2(1, 2)
localvec2=Vector2(3, 4)
print(vec1+vec2)

The output of the example above is:

 "Vector2(4.0, 6.0)"