[ENH] Add orient argument and split option to to_dict. (GH7840)

closes #7840 

Unlike the implementation offered in #7840, this version preserves the option to pass prefixes to the `orient` parameter.

I also rewrote the docstring to use the more readable list format from `pd.DataFrame.to_json`.
yep, that is good 
the blank line is indeed needed to have the list rendered as a list