DOC: Update docs to use sphinx deprecated directive
As an example:

```
sheetname : string, int, mixed list of strings/ints, or None, default 0
    .. deprecated:: 0.21.0
       Use `sheet_name` instead

```

Some examples that need to be replaced (line numbers, and maybe filenames will change)

```
doc/source/io.rst:140:  DEPRECATED: this argument will be removed in a future version. Please call
doc/source/io.rst:194:  DEPRECATED: use the ``skipfooter`` parameter instead, as they are identical
doc/source/io.rst:205:    DEPRECATED: this argument will be removed in a future version because its
doc/source/io.rst:208:  DEPRECATED: this argument will be removed in a future version
doc/source/io.rst:214:  DEPRECATED: this argument will be removed in a future version
doc/sphinxext/numpydoc/README.rst:49:- numpydoc_edit_link: bool  (DEPRECATED -- edit your HTML template instead)
pandas/_libs/tslib.pyx:1151:        DEPRECATED: use :meth:`to_pydatetime` instead.
pandas/core/common.py:551:    DEPRECATED: This is no longer needed, or working, in IPython 3 and above.
pandas/core/common.py:569:    DEPRECATED: This is no longer used in pandas, and won't work in IPython 3
pandas/core/categorical.py:394:        DEPRECATED: calling this method will raise an error in a
pandas/core/categorical.py:426:        DEPRECATED: Use ``Categorical`` instead.
pandas/core/categorical.py:1445:        DEPRECATED: use :meth:`Categorical.sort_values`. That function
pandas/core/categorical.py:1459:        DEPRECATED: use :meth:`Categorical.sort_values`. That function
pandas/core/dtypes/common.py:691:    DEPRECATED: This function will be removed in a future version.
pandas/core/dtypes/common.py:1490:    DEPRECATED: This function will be removed in a future version.
pandas/core/frame.py:3480:        DEPRECATED: use :meth:`DataFrame.sort_index`
pandas/core/generic.py:1325:            DEPRECATED: this parameter will be removed in a future version,
pandas/core/generic.py:3074:        DEPRECATED: consolidate will be an internal implementation only.
pandas/core/generic.py:3285:        raise_on_error : DEPRECATED use ``errors`` instead
pandas/core/generic.py:5544:        infer_dst : boolean, default False (DEPRECATED)
pandas/core/indexes/base.py:1011:        DEPRECATED: use :meth:`pandas.to_datetime` instead.
pandas/core/indexes/period.py:569:        DEPRECATED: use :meth:`to_timestamp` instead.
pandas/core/indexes/datetimes.py:200:    infer_dst : boolean, default False (DEPRECATED)
pandas/core/indexes/datetimes.py:1821:        infer_dst : boolean, default False (DEPRECATED)
pandas/core/panel4d.py:22:    DEPRECATED. Panel4D is deprecated and will be removed in a future version.
pandas/core/panelnd.py:12:    DEPRECATED. Panelnd is deprecated and will be removed in a future version.
pandas/core/series.py:853:        DEPRECATED: calling this method will raise an error in a
pandas/core/series.py:1943:        DEPRECATED: use :meth:`Series.sort_index`
pandas/core/sparse/array.py:394:            DEPRECATED: this argument will be removed in a future version
pandas/core/sparse/series.py:538:            DEPRECATED: this argument will be removed in a future version.
pandas/core/strings.py:481:    as_indexer : DEPRECATED
pandas/core/window.py:344:    how : string, default None (DEPRECATED)
pandas/core/window.py:352:    how : string, default None (DEPRECATED)
pandas/core/window.py:376:    freq : string or DateOffset object, optional (default None) (DEPRECATED)
pandas/core/window.py:573:        how : string, default to None (DEPRECATED)
pandas/core/window.py:738:        how : string, default to None (DEPRECATED)
pandas/core/window.py:866:    how : string, default 'max' (DEPRECATED)
pandas/core/window.py:880:    how : string, default 'min' (DEPRECATED)
pandas/core/window.py:898:    how : string, default 'median' (DEPRECATED)
pandas/core/window.py:1325:    freq : string or DateOffset object, optional (default None) (DEPRECATED)
pandas/core/window.py:1589:    freq : None or string alias / date offset object, default=None (DEPRECATED)
pandas/core/window.py:1723:        how : string, default to None (DEPRECATED)
pandas/io/excel.py:145:    DEPRECATED: for version 0.17+ index names will be automatically
pandas/io/parsers.py:108:    DEPRECATED: this argument will be removed in a future version. Please call
pandas/io/parsers.py:148:    DEPRECATED: use the `skipfooter` parameter instead, as they are identical
pandas/io/parsers.py:279:    DEPRECATED: this argument will be removed in a future version because its
pandas/io/parsers.py:282:    DEPRECATED: this argument will be removed in a future version
pandas/io/parsers.py:289:    DEPRECATED: this argument will be removed in a future version
pandas/io/sql.py:435:        DEPRECATED: this parameter will be removed in a future version
pandas/io/sql.py:487:        DEPRECATED: this parameter will be removed in a future version
pandas/io/sql.py:1548:        DEPRECATED: this parameter will be removed in a future version
pandas/io/stata.py:1410:    @Appender('DEPRECATED: ' + _data_method_doc)
```