Wren now has three classes of modules:
- The one magic "core" module that's built in and always needed.
- Auxiliary libraries like "meta" and "random". These do not have any
dependencies, so can be used even when you embed Wren inside an
application. But they're also optional and can be disabled if you
don't need them.
- CLI modules. These ones need libuv and are tied to the CLI wrapper
around the VM.
- Add an explicit va_list version. That lets variadic functions
forward to it.
- Fix a GC bug in wrenCall() with return values.
- Make the call API test not re-enter the VM.
- Test that a foreign method can return strings.
- Test that a foreign method can return a string with null bytes.
- Test wrenCall().
- Allow passing NULL for "v" to wrenCall().
- Allow "a" for passing an explicit length byte array to wrenCall().
