Follow-up version 2.0

[loicdiridollou]

This issue tackles some of the points in #624:

• Added Index.infer_objects() analogous to Series.infer_objects()
• Index set operations Index.union(), Index.intersection(), Index.difference(), and Index.symmetric_difference() now support sort=True, which will always return a sorted result, unlike the default sort=None which does not sort in some cases

The following ones are already addressed:

• Added support for decimal parameter when engine="pyarrow" in read_csv()
• Removed deprecated global option use_inf_as_null in favor of use_inf_as_na
• Removed deprecated module pandas.core.index
• Removed deprecated alias pandas.io.json.json_normalize
• Removed deprecated pandas.api.types.is_categorical()
• Removed deprecated argument null_color in Styler.highlight_null()
• Enforced deprecation disallowing passing non boolean argument to sort in concat()
• Removed argument index from the core.arrays.SparseArray constructor
• Remove argument squeeze from DataFrame.groupby() and Series.groupby()
• Remove arguments names and dtype from Index.copy() and levels and codes from MultiIndex.copy()
• Removed argument line_terminator from DataFrame.to_csv() and Series.to_csv(),
• Removed argument inplace from DataFrame.set_axis() and Series.set_axis()
• Disallow passing positional arguments to MultiIndex.set_levels() and MultiIndex.set_codes()
• Removed MultiIndex.is_lexsorted() and MultiIndex.lexsort_depth()
• Removed argument tz from Period.to_timestamp()
• Removed argument kind from Index.get_slice_bound(), Index.slice_indexer() and Index.slice_locs()
• Removed arguments prefix, squeeze, error_bad_lines and warn_bad_lines from read_csv()
• Disallow passing list key to Series.xs() and DataFrame.xs()
• Remove keywords convert_float and mangle_dupe_cols from read_excel()
• Remove keyword mangle_dupe_cols from read_csv() and read_table()