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
diff --git a/Doc/library/gc.rst b/Doc/library/gc.rst
index 153d8fb..722a0e8 100644
--- a/Doc/library/gc.rst
+++ b/Doc/library/gc.rst
@@ -181,7 +181,7 @@
    fork() call to make the gc copy-on-write friendly or to speed up collection.
    Also collection before a POSIX fork() call may free pages for future
    allocation which can cause copy-on-write too so it's advised to disable gc
-   in master process and freeze before fork and enable gc in child process.
+   in parent process and freeze before fork and enable gc in child process.
 
    .. versionadded:: 3.7
 
diff --git a/Doc/library/multiprocessing.rst b/Doc/library/multiprocessing.rst
index 504f3a1..a7d26f9 100644
--- a/Doc/library/multiprocessing.rst
+++ b/Doc/library/multiprocessing.rst
@@ -435,7 +435,7 @@
 
    (If you try this it will actually output three full tracebacks
    interleaved in a semi-random fashion, and then you may have to
-   stop the master process somehow.)
+   stop the parent process somehow.)
 
 
 Reference