Function get_environment

extlibs/sol3/include/sol/sol.hpp:23786–23790

	template <typename E = reference, typename T>
	basic_environment<E> get_environment(const T& target) {
		lua_State* L = target.lua_state();
		auto pp = stack::pop_n(L, stack::push_environment_of(target));
		return basic_environment<E>(L, -1);
	}

	struct this_environment {
		optional<environment> env;