Introduce instructions `pick` + `i` and `place` + `i`

[jan-ferdinand]

The two new instructions simplify manipulation of the operational stack. Instruction pick + i moves the indicated stack element to the top of the stack. Instruction place + i is its dual, moving the top of the stack to the indicated position.

	old op stack	new op stack
pick + i	e.g., _ d x c b a	e.g., _ d c b a x
place + i	e.g., _ d c b a x	e.g., _ d x c b a