Avoid a temporary buffer to create a bytes string: use
PyBytes_FromStringAndSize() to directly allocate a bytes object.
Cleanup also the code: PEP 7 formatting, move variable definitions
closer to where they are used. Fix assertion checking "j" index.
* bpo-22385: Support output separators in hex methods.
Also in binascii.hexlify aka b2a_hex.
The underlying implementation behind all hex generation in CPython uses the
same pystrhex.c implementation. This adds support to bytes, bytearray,
and memoryview objects.
The binascii module functions exist rather than being slated for deprecation
because they return bytes rather than requiring an intermediate step through a
str object.
This change was inspired by MicroPython which supports sep in its binascii
implementation (and does not yet support the .hex methods).
https://bugs.python.org/issue22385
