Panel data and datasets

Toolset panel_data: 3 tools.

Tool	What it does	Notes
`panel_dataset`	Returns a classic econometrics dataset bundled with the engine (or a simulated panel) as columns by name, with its description: variables, units and source.
`panel_structure`	Describes a long panel or applies the panel transforms the estimators use.
`panel_hac_bandwidth`	The automatic (data-driven) bandwidth for a HAC covariance with the chosen kernel, and the kernel weight on each lag at that bandwidth (or at the bandwidth given), as a series with a bar chart.

Inputs, limits and outputs are described in Fincept Panel. Full schemas: fincept_describe_tool.