Remove newState, newStateLibc, and setAllocF

[natecraddock]

It isn't clear if these functions are of any use. After the changes from #40, removing these functions is not required, but it could still make things cleaner.

The one benefit from removing these functions is the Lua.allocator() function can never fail by making it impossible to create a Lua state without a Zig allocator from Ziglua.