Added pop() function to `reference`
`stack.hpp` now has many more functions to properly handle user data
`types.hpp` now has `userdata_t` and `lightuserdata_t` to faciliate `stack`'s `pop` and `push` operations
Class binding functionality built into `table` and `state`, as well as placed in `userdata` class in `userdata.hpp`
demangling detail now present for clang, gcc, and MSVC (somewhat for MSVC)
Constructor arity still needs to be handled for `userdata<T>`
tests updated and passing
But! I left it on the `sol::function` type, because it's necessary to discard returns. The .call is still there, though, just incase you need it. <3
reverse_indices_builder is also there, to make sure we can push and pop without the lua api taking our types and breaking them for the std::tuple returns.
All is at it should be~
