Allow metatable operations on values of all types, and use the metatable

on strings as the string package, so that string functions can be called
with self (:) syntax. Autoload test case now inexplicably fails more,
but it was already broken.

src/test/res/metatables.lua

@@ -0,0 +1,5 @@
+-- The purpose of this test case is to demonstrate that
+-- basic metatable operations on non-table types work.
+-- i.e. that s.sub(s,...) could be used in place of string.sub(s,...)
+local s = "hello"
+print(s:sub(2,4))