bpo-34605: Avoid master/slave terms (GH-9101)

* Replace "master process" with "parent process"
* Replace "master option mappings" with "main option mappings"
* Replace "master pattern object" with "main pattern object"
* ssl: replace "master" with "server"
* And some other similar changes

Lib/sre_parse.py

@@ -72,7 +72,7 @@ class Verbose(Exception):
     pass
 
 class Pattern:
-    # master pattern object.  keeps track of global attributes
+    # main pattern object.  keeps track of global attributes
     def __init__(self):
         self.flags = 0
         self.groupdict = {}