Shuffle words

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Shuffle words rearrange items at the top of the data stack. They control the flow of data between words that perform actions.

The Cleave combinators, Spread combinators and Apply combinators are closely related to shuffle words and should be used instead where possible because they can result in clearer code; also, see the advice in Factor philosophy.

Removing stack elements:
• drop ( x -- )
• 2drop ( x y -- )
• 3drop ( x y z -- )
• nip ( x y -- y )
• 2nip ( x y z -- z )
Duplicating stack elements:
• dup ( x -- x x )
• 2dup ( x y -- x y x y )
• 3dup ( x y z -- x y z x y z )
• dupd ( x y -- x x y )
• over ( x y -- x y x )
• 2over ( x y z -- x y z x y )
• pick ( x y z -- x y z x )
• tuck ( x y -- y x y )
Permuting stack elements:
• swap ( x y -- y x )
• swapd ( x y z -- y x z )
• rot ( x y z -- y z x )
• -rot ( x y z -- z x y )
• spin ( x y z -- z y x )
• roll ( x y z t -- y z t x )
• -roll ( x y z t -- t x y z )