DOC: add whatsnew entry

Author: tacaswell

doc/source/whatsnew/v0.21.0.txt

@@ -128,6 +128,8 @@ Other Enhancements
 - :func:`DataFrame.add_prefix` and :func:`DataFrame.add_suffix` now accept strings containing the '%' character. (:issue:`17151`)
 - `read_*` methods can now infer compression from non-string paths, such as ``pathlib.Path`` objects (:issue:`17206`).
 - :func:`pd.read_sas()` now recognizes much more of the most frequently used date (datetime) formats in SAS7BDAT files (:issue:`15871`).
+- :func:`DataFrame.items` is present in both Python 2 and 3 and is lazy in all cases (:issue:`13918`, :issue:`17213`)
+
 
 .. _whatsnew_0210.api_breaking: