Add `proto` and `upval` types from lua 5.1

[Askaholic]

Lua 5.1 adds 2 new types, "proto" and "upval" which GPG backported into their version of lua.

https://www.lua.org/source/5.1/ltm.c.html

NOTE: Github mirror is not on the most recent version of lua 5.1
https://github.com/lua/lua/blob/98194db4295726069137d13b8d24fca8cbf892b6/ltm.c#L26