Formatting features

1.  \null [string] - Show or set NULL representation
2.  \f [string] Show or set field separator
3.  \t [on|off] Toggle or set tuple only output
4.  \a [on|off] Toggle or set aligned output
5.  rightmost column is no longer padded
Tests added and updated

There are three cases in this block doing the "on"/"off"/error parsing. Maybe a helper function is in order?