Orderby array_multisort

allows piped orderby, sort and sort_type
Sort_types: string, numeric, lowercase

Signed-off-by: GDmac <grdalenoort@gmail.com>
don't add non-existing orderby keys to $list

Signed-off-by: GDmac <grdalenoort@gmail.com>
Merge pull request #71 from GDmac/feature-multisort