text: Title: Deprecate functions ?
  Body: Central point to discuss functions to deprecate, if any?
  
  - [x] `process_text` - `transform_columns` covers this very well
  - [x]  `impute` vs `fill_empty` - `impute` has the advantage of extra statistics functions (mean, mode, ...)
  - [x] `rename_columns` - use pandas `rename`
  - [x] `rename_column` - use `pd.rename`
  - [x] `remove_columns` - use `pd.drop` or `select`
  - [x] `filter_on` - use `query` or `select`
  - [x] `fill_direction` - use `transform_columns` or `pd.DataFrame.assign`
  - [x] `groupby_agg` - use `transform_columns` - once `by` is implemented
  - [x] `then` - use `pd.DataFrame.pipe`
  - [x] `to_datetime` - use `jn.transform_columns`
  - [x] `pivot_wider` - use `pd.DataFrame.pivot`