def divmod(other)
      if Quantity===other
        @value.divmod( @unit.convert(other) )
      else
        d,m = @value.divmod(other)
        [ self.class.new( d, @expr, @unit ),
          self.class.new( m, @expr, @unit ) ]
      end
    end
def divmod(other)
      if Quantity===other
        @value.divmod( @unit.convert(other) )
      else
        d,m = @value.divmod(other)
        [ self.class.new( d, @expr, @unit ),
          self.class.new( m, @expr, @unit ) ]
      end
    end
Division with Modulo.
 * If the +other+ param is Phys::Quantity,
   +other+ is converted to the unit of +self+,
   and returns +divmod+ of values.
 * If the +other+ param is *not* Phys::Quantity,
   +other+ is regarded as dimensionless,
   and returns +divmod+ of Phys::Quantity.
 @param  [Object] other
 @return [Array] result of +divmod+, an array of [quotient, modulo].
 @raise  [Phys::UnitError] if unit conversion is failed.