Safe API for calling lua functions from rust

[volt0]

This will require implementing a wrapper structure around the lua state. It should be possible to get an instance of the structure from the global state. Also add the call method, which takes as input a reference to the structure containing the arguments and returns a Result containing the result of the lua function or an error.

For example:

#[derive(ToLuaTable)]
struct User {
    username: String,
    email: String,
    id: u64,
    active: bool,
}

#[derive(FromLuaTable)]
struct CreateUserResult {
    ok: bool,
    id: u64,
}

...

let lua = Lua::global()
let result: CreateUserResult = lua.call("some_module.create_user", &user)?;
if result.ok {
    ...
}

-- some_module.lua
function create_user(username, email, id, active)
    ...
    return true, id
end

[t1-10]

Implemented in v5.0.0