DOC: clean-up whatsnew file for 0.21.1 (#18690)

(cherry picked from commit 16de5f9)

Author: jorisvandenbossche

doc/source/whatsnew/v0.21.1.txt

@@ -3,9 +3,23 @@
 v0.21.1
 -------
 
-This is a minor release from 0.21.1 and includes a number of deprecations, new
-features, enhancements, and performance improvements along with a large number
-of bug fixes. We recommend that all users upgrade to this version.
+This is a minor bug-fix release in the 0.21.x series and includes some small regression fixes,
+bug fixes and performance improvements.
+We recommend that all users upgrade to this version.
+
+Highlights include:
+
+- Temporarily restore matplotlib datetime plotting functionality. This should
+  resolve issues for users who relied implicitly on pandas to plot datetimes
+  with matplotlib. See :ref:`here <whatsnew_0211.special>`.
+- Improvements to the Parquet IO functions introduced in 0.21.0. See
+  :ref:`here <whatsnew_0211.enhancements.parquet>`.
+
+
+.. contents:: What's new in v0.21.1
+    :local:
+    :backlinks: none
+
 
 .. _whatsnew_0211.special:
 
@@ -42,9 +56,13 @@ registering them when they want them.
 New features
 ~~~~~~~~~~~~
 
--
--
--
+.. _whatsnew_0211.enhancements.parquet:
+
+Improvements to the Parquet IO functionality
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+- :func:`read_parquet` now allows to specify the columns to read from a parquet file (:issue:`18154`)
+- :func:`read_parquet` now allows to specify kwargs which are passed to the respective engine (:issue:`18216`)
 
 .. _whatsnew_0211.enhancements.other:
 
@@ -53,7 +71,6 @@ Other Enhancements
 
 - :meth:`Timestamp.timestamp` is now available in Python 2.7. (:issue:`17329`)
 - :class:`Grouper` and :class:`TimeGrouper` now have a friendly repr output (:issue:`18203`).
--
 
 .. _whatsnew_0211.deprecations:
 
@@ -69,17 +86,6 @@ Performance Improvements
 ~~~~~~~~~~~~~~~~~~~~~~~~
 
 - Improved performance of plotting large series/dataframes (:issue:`18236`).
--
--
-
-.. _whatsnew_0211.docs:
-
-Documentation Changes
-~~~~~~~~~~~~~~~~~~~~~
-
--
--
--
 
 .. _whatsnew_0211.bug_fixes:
 
@@ -97,7 +103,6 @@ Conversion
 - Bug in :func:`DataFrame.to_dict` where columns of datetime that are tz-aware were not converted to required arrays when used with ``orient='records'``, raising``TypeError` (:issue:`18372`)
 - Bug in :class:`DateTimeIndex` and :meth:`date_range` where mismatching tz-aware ``start`` and ``end`` timezones would not raise an err if ``end.tzinfo`` is None (:issue:`18431`)
 - Bug in :meth:`Series.fillna` which raised when passed a long integer on Python 2 (:issue:`18159`).
--
 
 Indexing
 ^^^^^^^^
@@ -107,7 +112,6 @@ Indexing
 - Bug in :class:`IntervalIndex` constructor when a list of intervals is passed with non-default ``closed`` (:issue:`18334`)
 - Bug in ``Index.putmask`` when an invalid mask passed (:issue:`18368`)
 - Bug in masked assignment of a ``timedelta64[ns]`` dtype ``Series``, incorrectly coerced to float (:issue:`18493`)
--
 
 I/O
 ^^^
@@ -117,8 +121,6 @@ I/O
 - Bug in :func:`read_csv` for handling null values in index columns when specifying ``na_filter=False`` (:issue:`5239`)
 - Bug in :func:`read_csv` when reading numeric category fields with high cardinality (:issue:`18186`)
 - Bug in :meth:`DataFrame.to_csv` when the table had ``MultiIndex`` columns, and a list of strings was passed in for ``header`` (:issue:`5539`)
-- :func:`read_parquet` now allows to specify the columns to read from a parquet file (:issue:`18154`)
-- :func:`read_parquet` now allows to specify kwargs which are passed to the respective engine (:issue:`18216`)
 - Bug in parsing integer datetime-like columns with specified format in ``read_sql`` (:issue:`17855`).
 - Bug in :meth:`DataFrame.to_msgpack` when serializing data of the numpy.bool_ datatype (:issue:`18390`)
 - Bug in :func:`read_json` not decoding when reading line deliminted JSON from S3 (:issue:`17200`)
@@ -130,8 +132,6 @@ Plotting
 ^^^^^^^^
 
 - Bug in ``DataFrame.plot()`` and ``Series.plot()`` with :class:`DatetimeIndex` where a figure generated by them is not pickleable in Python 3 (:issue:`18439`)
--
--
 
 Groupby/Resample/Rolling
 ^^^^^^^^^^^^^^^^^^^^^^^^
@@ -140,15 +140,6 @@ Groupby/Resample/Rolling
 - Bug in ``DataFrame.resample(...)`` when there is a time change (DST) and resampling frequecy is 12h or higher (:issue:`15549`)
 - Bug in ``pd.DataFrameGroupBy.count()`` when counting over a datetimelike column (:issue:`13393`)
 - Bug in ``rolling.var`` where calculation is inaccurate with a zero-valued array (:issue:`18430`)
--
--
-
-Sparse
-^^^^^^
-
--
--
--
 
 Reshaping
 ^^^^^^^^^
@@ -164,7 +155,6 @@ Numeric
 - Bug in ``pd.Series.rolling.skew()`` and ``rolling.kurt()`` with all equal values has floating issue (:issue:`18044`)
 - Bug in :class:`TimedeltaIndex` subtraction could incorrectly overflow when ``NaT`` is present (:issue:`17791`)
 - Bug in :class:`DatetimeIndex` subtracting datetimelike from DatetimeIndex could fail to overflow (:issue:`18020`)
--
 
 Categorical
 ^^^^^^^^^^^
@@ -180,9 +170,3 @@ String
 ^^^^^^
 
 - :meth:`Series.str.split()` will now propogate ``NaN`` values across all expanded columns instead of ``None`` (:issue:`18450`)
-
-Other
-^^^^^
-
--
--