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

Minor nit: set is usually used instead of change for the modifying methods. This class has a mixture that would be nice to get consistent on.