Allow non-feather files to be inputted and outputted #14
Description
Feather should be the default (and preferred) option to ensure that variable types are preserved.
Where the outputs from this action are intended to be directly sent for release, a csv file should be allowed.
Rarely, it may be appropriate to allow csv files as the input dataset, but we should probably not include parsing options as this will overload the action. Instead, provide some basic advice about what the parser (probably read_csv) will do, and to recommend feather!