dfr ls for dataframe

Lists stored dataframes.

Signature

> dfr ls

Input/output types:

input	output
any	any

Examples

Creates a new dataframe and shows it in the dataframe list

> let test = ([[a b];[1 2] [3 4]] | dfr into-df);
    ls

Tips: Dataframe commands were not shipped in the official binaries by default, you have to build it with --features=dataframe flag