[docs] Improve Doc/library/xmlrpc.client.rst (issue 26889)

[tjreedy at udel.edu]

https://bugs.python.org/review/26889/diff/17111/Doc/library/xmlrpc.client.rst
File Doc/library/xmlrpc.client.rst (right):

https://bugs.python.org/review/26889/diff/17111/Doc/library/xmlrpc.client.rst#newcode17
Doc/library/xmlrpc.client.rst:17: XML-RPC is a Remote Procedure Call
method that uses XML passed via HTTP as a
HTTP(S) better?

https://bugs.python.org/review/26889/diff/17111/Doc/library/xmlrpc.client.rst#newcode49
Doc/library/xmlrpc.client.rst:49: 
New blank line separates instance construction parameters above from
instance use parameters.  Good.  I think you could even something like
"The following parameters govern the use of the returned proxy
instance."

https://bugs.python.org/review/26889/diff/17111/Doc/library/xmlrpc.client.rst#newcode53
Doc/library/xmlrpc.client.rst:53: all clients and servers; see
http://ontosys.com/xml-rpc/extensions.php for a
New link displays page with "Wayback Machine doesn't have that page
archived."  Is any more description really needed? Can you just
incorporate it?

https://bugs.python.org/review/26889/diff/17111/Doc/library/xmlrpc.client.rst#newcode76
Doc/library/xmlrpc.client.rst:76: 
Not sure that deletion of sentence is an improvement.  See tracker post.

https://bugs.python.org/review/26889/