PSTokenizer is now an indipendent object behaving like a StringIO.StringIO: it has `read` and `close` methods, as well as `buf`, `pos` and `len` attributes.
The input data is a string of bytes, and the output tokens are ascii-decoded unicode strings.
(I removed "__main__" as it was using a non-py23 EasyDialogs module)
See https://github.com/behdad/fonttools/issues/393.
Related to https://github.com/behdad/fonttools/issues/391.