Modify _PyBytes_DecodeEscapeRecode() to use _PyBytesAPI

* Don't overallocate by 400% when recode is needed: only overallocate on demand
  using _PyBytesWriter.
* Use _PyLong_DigitValue to convert hexadecimal digit to int
* Create _PyBytes_DecodeEscapeRecode() subfunction
2 files changed