Re: WIP Incremental JSON Parser

This new return path...

> +       if (!tok_done)
> +       {
> +           if (lex->inc_state->is_last_chunk)
> +               return JSON_INVALID_TOKEN;

...also needs to set the token pointers. See one approach in the
attached diff, which additionally asserts that we've consumed the
entire chunk in this case, along with a handful of new tests.