Docs tweaks for contextlib additions
Issue #19219 Remove a lot of "retval = NULL" statements, now that retval
is pre-initialized to that value.  Test show a 5% speedup as a bonus.
Issue #17827: Document codecs.encode and codecs.decode
Issue #18919: Unified and extended tests for audio modules: aifc, sunau and
wave.
Issue #17827: document codecs.encode and codecs.decode

- Merge from 3.3
- Added to What's New since these are more important in 3.x,
  as the bytes<->bytes and str<->str codecs don't fit the
  text model convenience methods in 3.x the way they did the
  basestring<->basestring methods in the 2.x text model
- Included under Library in Misc/NEWS for the same reason
Issue #18919: Unified and extended tests for audio modules: aifc, sunau and
wave.
Merge heads
Merge heads
Null merge
Catch a few extra error cases in marshal.c
Issue #19198: Improved cross-references in the cgi module documentation.
Issue #19198: Improved cross-references in the cgi module documentation.
Issue #19203: Improved cross-references in the curses howto.
Merge heads
Issue #19203: Improved cross-references in the curses howto.
Refer to strftime(3) manpage for platform specific format codes.

Suggested by Skip Montanaro on docs@.
merge with 3.3
Improve #19204: Improved cross-references in the urllib package documentation.
Improve #19204: Improved cross-references in the urllib package documentation.
Issue #19207: Improved cross-references in the os, os.path, and posix modules
documentation.