Add a simple test program to verify that the hslua bindings actually work

When linking against the system's lua library, it's possible that the
hslua library is broken (despite the fact that build succeeds) because
the system's lua shared library lacks certain symbols, i.e.:

  HShslua-0.3.7.o: unknown symbol `lua_neutralize_longjmp'

The included test program catches those issues.