Migration to 2.0 - Deprecation in Resample

[loicdiridollou]

Incremental part of #624

• Deprecated unused arguments *args and **kwargs in Resampler
• Deprecated Series.pad()
• Deprecated Series.backfill()
• Deprecated DataFrame.pad()
• Deprecated DataFrame.backfill()
• Deprecated close(). Use StataReader as a context manager instead
• Removed Int64Index, UInt64Index and Float64Index.
• Deprecated argument infer_datetime_format in to_datetime() and read_csv(), as a strict version of it is now the default
• Deprecated pandas.io.sql.execute()