Import serpent (#1527)
Import serpent (#1527)

* Import serpent (https://github.com/pkulchenko/serpent)
* We don't build w/ Lua 5.2 compat, so keep using the real pairs fn, as I don't recall if next is JIT'ed
* Make LuaCheck ignore serpent (It's unhappy about the shadowed variables, mostly).
NiLuJe/koreader-base,koreader/koreader-base,NiLuJe/koreader-base,koreader/koreader-base,NiLuJe/koreader-base,koreader/koreader-base,koreader/koreader-base,NiLuJe/koreader-base