Remove _random.Random.randbytes(): the C implementation of
randbytes(). Implement the method in Python to ease subclassing:
randbytes() now directly reuses getrandbits().
Add random.randbytes() function and random.Random.randbytes()
method to generate random bytes.
Modify secrets.token_bytes() to use SystemRandom.randbytes()
rather than calling directly os.urandom().
Rename also genrand_int32() to genrand_uint32(), since it returns an
unsigned 32-bit integer, not a signed integer.
The _random module is now built with Py_BUILD_CORE_MODULE defined.
Serhiy Storchaka
Dong-hee Na
Victor Stinner
Pablo Galindo