Merge: #25495: Clarify b2a_base64 documentation vis 57 bytes.

In 3.6 the parameter to control the appending of the newline was finally
added, so I dropped the historical note about why a new line was always
appended.

diff --cc Doc/library/binascii.rst
index 0cd18b1740e0c2a4effa7f7e08d19fb585e5fe01,ff2bddaf9d7f2aed03c50e3119ed6998984810da..632ecf7f0f6b95cd3085adf9b2025fb7f28bbe40
--- 1/Doc/library/binascii.rst
--- 2/Doc/library/binascii.rst
+++ b/Doc/library/binascii.rst
@@@ -52,16 -52,13 +52,14 @@@ The :mod:`binascii` module defines the 
     than one line may be passed at a time.
  
  
 -.. function:: b2a_base64(data)
 +.. function:: b2a_base64(data, \*, newline=True)
  
     Convert binary data to a line of ASCII characters in base64 coding. The return
 -   value is the converted line, including a newline char.  The newline is
 -   added because the original use case for this function was to feed it a
 -   series of 57 byte input lines to get output lines that conform to the
 -   MIME-base64 standard.  Otherwise the output conforms to :rfc:`3548`.
 +   value is the converted line, including a newline char if *newline* is
-    true. The length of *data* should be at most 57 to adhere to the
-    base64 standard.
- 
++   true.  The output of this function conforms to :rfc:`3548`.
 +
 +   .. versionchanged:: 3.6
 +      Added the *newline* parameter.
  
  
  .. function:: a2b_qp(data, header=False)