Method copy

include/sol/stack_reference.hpp:115–117

		}

		stateless_stack_reference copy(lua_State* L_) const noexcept {
			return stateless_stack_reference(L_, raw_index(m_index));
		}

		void copy_assign(lua_State*, const stateless_stack_reference& right) noexcept {
			m_index = right.m_index;