[docs] Python 3 crc32 documentation clarifications (issue 22341)

[storchaka at gmail.com]

https://bugs.python.org/review/22341/diff/13462/Doc/library/binascii.rst
File Doc/library/binascii.rst (right):

https://bugs.python.org/review/22341/diff/13462/Doc/library/binascii.rst#newcode125
Doc/library/binascii.rst:125: the given *crc*.  The default initial
value is zero.  The algorithm
May be just write the signature as crc32(data, crc=0) and drop the
sentence about the default value?

https://bugs.python.org/review/22341/diff/13462/Doc/library/zlib.rst
File Doc/library/zlib.rst (right):

https://bugs.python.org/review/22341/diff/13462/Doc/library/zlib.rst#newcode36
Doc/library/zlib.rst:36: the checksum; otherwise, a default value of 1
is used.
Same as for binascii.crc32().

https://bugs.python.org/review/22341/diff/13462/Doc/library/zlib.rst#newcode96
Doc/library/zlib.rst:96: default value of zero is used.
Same as above.

https://bugs.python.org/review/22341/