Add ScriptValue::Tuple(Vec<ScriptValue>) variant.

[shanecelis]

Problem

Some Lua APIs can pass back multiple values that are not a list. They may look like this:

x, y = cursor()

Currently one can't implement this in Rust.

Solution

What I'd suggest is to add a variant to ScriptValue called Tuple(Vec<ScriptValue>) which holds the same data type as ScriptValue::List then pass back the multiple values.

Work Around

The work around I've used is to implement _cursor() in Rust that returns a list and then in Lua add the following function:

function cursor()
  local l = _cursor()
  return l[1], l[2]
end

Considerations

I don't know if Lua is the only supported language that supports multiple return values. But one would need a policy on what to do if the language does not support it. I'd suggest languages that don't support multiple return values should treat ScriptValue::List and ScriptValue::Tuple the same.