updating whatsnew docs

Author: ArkadeepAdhikari

doc/source/whatsnew/v0.15.0.rst

@@ -852,7 +852,7 @@ Other notable API changes:
      A value is trying to be set on a copy of a slice from a DataFrame.
      Try using .loc[row_indexer,col_indexer] = value instead
 
-     See the caveats in the documentation: https://pandas.pydata.org/pandas-docs/stable/indexing.html#indexing-view-versus-copy
+     See the caveats in the documentation: :ref:`Indexing <indexing>`
 
 - ``merge``, ``DataFrame.merge``, and ``ordered_merge`` now return the same type
   as the ``left`` argument (:issue:`7737`).

doc/source/whatsnew/v0.16.0.rst

@@ -529,6 +529,7 @@ Deprecations
   but more refined functionality (:issue:`3445`).
   The documentation includes some examples how to convert your existing code
   from ``rplot`` to seaborn `here <https://pandas.pydata.org/pandas-docs/version/0.18.1/visualization.html#trellis-plotting-interface>`__.
+
 - The ``pandas.sandbox.qtpandas`` interface is deprecated and will be removed in a future version.
   We refer users to the external package `pandas-qt <https://github.com/datalyze-solutions/pandas-qt>`_. (:issue:`9615`)
 

doc/source/whatsnew/v0.21.0.rst

@@ -470,7 +470,7 @@ Current behavior
    KeyError in the future, you can use .reindex() as an alternative.
 
    See the documentation here:
-   https://pandas.pydata.org/pandas-docs/stable/indexing.html#deprecate-loc-reindex-listlike
+   :ref:`Indexing <indexing>`
 
    Out[4]:
    1    2.0