v		input view
start		index of first row
step		step size from one row to the next
count		number of rows in result

Slice returns a view containing every step'th row from v, starting at index start and continuing count times.

If the start index is negative, it is treated as end-relative. Use a negative step for reverse indexing or zero to repeat a single row.

Indexing is circular: when indexing past either end of v, the index wraps around to the other end. If v has no rows, then neither has the result.

set v [view A def {a b c}]

view $v slice 1 0 2

	A
0	b
1	b

view $v slice -1 -1 2

	A
0	c
1	b

view $v slice 0 2 3

	A
0	a
1	c
2	b