Support multiple arguments in row

[bluss]

Extend row in a logical direction prompted by #16 -- accept more than one argument.

// this
row([A & B], [C], [D & E])

// is the same as this
row([A & B & C & D & E])

// and this
row(table.cell[A], [B & C])

// is the same as this
row([A & B & C])