API: Have pd.pivot mirror pivot instead of pivot_simple
To pivot, there's currently:

`pd.pivot_table / df.pivot_table`
https://github.com/pandas-dev/pandas/blob/d30c4a0696d5fbdc3c7ce36a9b9b19224a557e09/pandas/core/reshape/pivot.py#L28

`df.pivot`
https://github.com/pandas-dev/pandas/blob/d30c4a0696d5fbdc3c7ce36a9b9b19224a557e09/pandas/core/reshape/reshape.py#L386

`pivot_simple` (Importable at the top level as `pd.pivot`)
https://github.com/pandas-dev/pandas/blob/d30c4a0696d5fbdc3c7ce36a9b9b19224a557e09/pandas/core/reshape/reshape.py#L411

I'm not sure why `pd.pivot` currently doesn't mirror `df.pivot` like how `pd.pivot_table` mirrors `df.pivot_table`, but it would clearer if these were in sync. 