Add list-ops exercise

[ErikSchierboom]

This was surprisingly easy.

[glennj]

How about a little helper word?

Suggested change

	"empty list"
	( [] ( 2 n:/mod drop 1 n:= ) filter )
	[]
	equal?
	"non-empty list"
	( [1, 2, 3, 5] ( 2 n:/mod drop 1 n:= ) filter )
	[1, 3, 5]
	equal?
	: odd? \ n -- t
	2 n:/mod drop 1 n:=
	;
	"empty list"
	( [] ' odd? filter )
	[]
	equal?
	"non-empty list"
	( [1, 2, 3, 5] ' odd? filter )
	[1, 3, 5]
	equal?