DOC: Fixing broken references in the docs (pandas-dev#24497)

Author: datapythonista

doc/source/advanced.rst

@@ -921,7 +921,7 @@ If you need integer based selection, you should use ``iloc``:
 
    dfir.iloc[0:5]
 
-.. _indexing.intervallindex:
+.. _advanced.intervallindex:
 
 IntervalIndex
 ~~~~~~~~~~~~~

doc/source/basics.rst

@@ -156,7 +156,7 @@ to these in old code bases and online. Going forward, we recommend avoiding
 ``.values`` and using ``.array`` or ``.to_numpy()``. ``.values`` has the following
 drawbacks:
 
-1. When your Series contains an :ref:`extension type <extending.extension-type>`, it's
+1. When your Series contains an :ref:`extension type <extending.extension-types>`, it's
    unclear whether :attr:`Series.values` returns a NumPy array or the extension array.
    :attr:`Series.array` will always return an ``ExtensionArray``, and will never
    copy data. :meth:`Series.to_numpy` will always return a NumPy array,

doc/source/ecosystem.rst

@@ -142,7 +142,8 @@ which are utilized by Jupyter Notebook for displaying
 (Note: HTML tables may or may not be
 compatible with non-HTML Jupyter output formats.)
 
-See :ref:`Options and Settings <options>` and :ref:`<options.available>`
+See :ref:`Options and Settings <options>` and
+:ref:`Available Options <options.available>`
 for pandas ``display.`` settings.
 
 `quantopian/qgrid <https://github.com/quantopian/qgrid>`__

pandas/core/groupby/groupby.py

@@ -1334,7 +1334,7 @@ def resample(self, rule, *args, **kwargs):
         Given a grouper, the function resamples it according to a string
         "string" -> "frequency".
 
-        See the :ref:`frequency aliases <timeseries.offset-aliases>`
+        See the :ref:`frequency aliases <timeseries.offset_aliases>`
         documentation for more details.
 
         Parameters