bpo-30794: added kill() method to multiprocessing.Process (#2528)

* bpo-30794: added kill() method to multiprocessing.Process

* Added entries to documentation and NEWS

* Refactored test_terminate and test_kill

* Fix SIGTERM and SIGKILL being used on Windows for the tests

* Added "versionadded" marker to the documentation

* Fix trailing whitespace in doc
diff --git a/Doc/library/multiprocessing.rst b/Doc/library/multiprocessing.rst
index 5265639..9318a75 100644
--- a/Doc/library/multiprocessing.rst
+++ b/Doc/library/multiprocessing.rst
@@ -598,6 +598,12 @@
          acquired a lock or semaphore etc. then terminating it is liable to
          cause other processes to deadlock.
 
+   .. method:: kill()
+
+      Same as :meth:`terminate()` but using the ``SIGKILL`` signal on Unix.
+
+      .. versionadded:: 3.7
+
    .. method:: close()
 
       Close the :class:`Process` object, releasing all resources associated