[pp:metadata] add 'newline' option (#8439)

* Add configuration setting to control newline characters in metadata.
* update docs/configuration
* introduce 'open()' method
* add 'newline' test

docs/configuration.rst

@@ -8225,7 +8225,7 @@ metadata.open
 -------------
 Type
     ``string``
-Defsult
+Default
     ``"w"``
 Description
     The ``mode`` in which metadata files get opened.
@@ -8241,7 +8241,7 @@ metadata.encoding
 -----------------
 Type
     ``string``
-Defsult
+Default
     ``"utf-8"``
 Description
     Name of the encoding used to encode a file's content.
@@ -8249,6 +8249,29 @@ Description
     See the ``encoding`` argument of |open()|_ for further details.
 
 
+metadata.newline
+-----------------
+Type
+    ``string``
+Default
+    ``null``
+Description
+    The newline sequence used in metadata files.
+
+    If ``null``, any ``\n`` characters
+    written are translated to the system default line separator.
+
+    See the ``newline`` argument of |open()|_ for further details.
+Supported Values
+    ``null``
+        Any ``\n`` characters
+        written are translated to the system default line separator.
+    ``""`` | ``"\n"``
+        Don't replace newline characters.
+    ``"\r"`` | ``"\r\n"``
+        Replace newline characters with the given sequence.
+
+
 metadata.private
 ----------------
 Type