Support Operator Overloading LuaMetamethods in LuaObjects #104

I would love the ability to make a LuaObject class that can handle operators differently based on the type being passed in.
An example being a Vector class that you can choose to multiply by either another Vector, or a double scalar:

-- Vector = Vector * Vector
local vec = Vector(1, 2, 3) * Vector(3, 2, 1)

-- Vector = Vector * double
local vec2 = Vector(1, 2, 3) * 10.0

I'd imagine declaring such a set up could look something like this, where each different function signature all share the same LuaMetamethod attribute

  [LuaMetamethod(LuaObjectMetamethod.Mul)]
  public static LuaVector MulVecVec(LuaVector aVec, LuaVector bVec)
  {
      return new LuaVector(aVec.vector * bVec.vector);
  }

  [LuaMetamethod(LuaObjectMetamethod.Mul)]
  public static LuaVector MulVecFloat(LuaVector aVec, double scalar)
  {
      return new LuaVector(aVec.vector * scalar);
  }

But understandably right now it complains about there already being a 'Mul' metamethod declared.

I can work around the issue by declaring a single metamethod that accepts LuaValues as parameters, but that requires manually checking the type of each argument which is pretty tedious (especially when there's other similar overloads for other operators).

Thank you (and this library rules)