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

Doc/library/codecs.rst

@@ -22,6 +22,25 @@ manages the codec and error handling lookup process.
 
 It defines the following functions:
 
+.. function:: encode(obj, encoding='utf-8', errors='strict')
+
+   Encodes *obj* using the codec registered for *encoding*.
+
+   *Errors* may be given to set the desired error handling scheme. The
+   default error handler is ``strict`` meaning that encoding errors raise
+   :exc:`ValueError` (or a more codec specific subclass, such as
+   :exc:`UnicodeEncodeError`). Refer to :ref:`codec-base-classes` for more
+   information on codec error handling.
+
+.. function:: decode(obj, encoding='utf-8', errors='strict')
+
+   Decodes *obj* using the codec registered for *encoding*.
+
+   *Errors* may be given to set the desired error handling scheme. The
+   default error handler is ``strict`` meaning that decoding errors raise
+   :exc:`ValueError` (or a more codec specific subclass, such as
+   :exc:`UnicodeDecodeError`). Refer to :ref:`codec-base-classes` for more
+   information on codec error handling.
 
 .. function:: register(search_function)