ENH/API: DataFrame.unstack() support for dropna and sequentially

[seth-p]

Add dropna and sequentially parameters to DataFrame.unstack(), to match DataFrame.stack(). For backwards compatibility, these should default to dropna=False and sequentially=False -- which are different from the defaults for DataFrame.stack().

[mroeschke]

Looks like this feature request hasn't gotten much traction over the years so closing. Happy to reopen if renewed intereset