Issue #6856: Add a filter keyword argument to TarFile.add().

The filter argument must be a function that takes a TarInfo
object argument, changes it and returns it again. If the
function returns None the TarInfo object will be excluded
from the archive.
The exclude argument is deprecated from now on, because it
does something similar but is not as flexible.
diff --git a/Misc/NEWS b/Misc/NEWS
index 4c38218..734bddf 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -366,6 +366,8 @@
 Library
 -------
 
+- Issue #6856: Add a filter keyword argument to TarFile.add().
+
 - Issue #6163: Fixed HP-UX runtime library dir options in
   distutils.unixcompiler. Initial patch by Sridhar Ratnakumar and
   Michael Haubenwallner.