Add support fo thrax for TN? about chinese_text_normalization

[dophist]

@npuichigo Hi, Yuchao, you are right, and it should be done in proper time.

The reasons that I haven't done it yet:

1. For now in speech recognition context, I use TN primarily for offline text processing, which involves other text processing scripts(such as data cleaning, simplified/traditional chinese conversion etc), keeping TN a simple python program is convenient.
2. For recognition, TN is not a runtime module (ITN is), efficiency is not a problem.

On the other hand when it comes to speech synthesis context, TN is definitely a runtime module and it should be done in thrax and sparrowhawks as you said.

A PR would be welcomed if any one can start some works on thrax TN rewriting rules, it shouldn't be very difficult with references to those ITN rules that I've done.