Process one text `t` with tokenizer `tok`.

def process_text(self, t:str, tok:BaseTokenizer) -> List[str]:
        "Process one text `t` with tokenizer `tok`."
        for rule in self.pre_rules: t = rule(t)
        toks = tok.tokenizer(t)
        for rule in self.post_rules: toks = rule(toks)
        return toks