[Feature] acro.pivot_table should support more of the underlying pandas functionality

[jim-smith]

Is your feature request related to a problem? Please describe.
currently (and in the ontology driven version) acro does not support the full pivot_table functionality, for example support for:

• groupers /list of groupers as options for index and columns
• multiple columns in values
• multiple aggregation funcs and dicts of {column:aggfunc}
• **kwargs that gets passed through to aggfuncs

Describe the solution you'd like
richer support

Describe alternatives you've considered
none

Additional context
Marked as blocked by the ontology-driven refactoring - no point in doing it then having to rewrite