A `FromLuaOwned` derive macro akin to `FromLua`

[sxyazi]

I have a FromLuaOwned derive macro that's like mlua's FromLua, but it calls userdata.take() instead of userdata.borrow().clone().

It saves me from some code duplication - do you think it's worth adding into mlua proper? If one needs it won't have to implement it themselves and deal with creating a separate crate (proc macros need [lib] proc-macro = true).

[khvzak]

There are also couple of other options too:

1. Instead of a new derive, add an attribute, e.g. #[mlua(from_lua = "take")]
2. Use a type wrapper UserDataTake<MyType> which would allow to take ownership of the userdata.

The later option allow to choose behaviour based on scope. I need to think about it.