Optionally link functions at compile-time

[PhilipRoman]

There should be an option to bypass hash-table lookup for the standard library. Sample code:

local x = tonumber(io.read()) + 1

Currently would generate this:

Object x = add(call(getglobal("tonumber"), call(index(getglobal("io"), "read"))), 1);

If the user is willing to sacrifice the ability to dynamically replace these functions, we could instead generate code like this:

int x = __tonumber(_ioread()) + 1

A similar mechanism could be used in implementing FFI (#18)