[docs] base64 "legacy" functions violate RFC 3548 (issue 1753718)

[vadmium+py at gmail.com]

http://bugs.python.org/review/1753718/diff/16115/Doc/library/base64.rst
File Doc/library/base64.rst (right):

http://bugs.python.org/review/1753718/diff/16115/Doc/library/base64.rst#newcode34
Doc/library/base64.rst:34: interface does not implement :rfc:`3548`.
In my mind, MIME’s transfer encoding is an application of RFC 3548; it
does implement base 64 under the covers. The real point is it just adds
line breaking on top. What about:

“. . . and adds newlines every 76 characters. The legacy interface
implements MIME’s *base64* transfer encoding, as per :rfc:`2045`.”

http://bugs.python.org/review/1753718/