Do we have a shift operation for array elements in Nim like this one? Well, now
we have.
The filling with default value: I am using a compiler initialized var to get
the default. Is that the suggested way?
```nim
proc shift[T](a: var openarray[T]; d: int) =
## Shift a right by d places for positive d or
## left for negative d.
## Shifted in elements are filled with default value.
var
h: T
j: int
if d > 0: # right shift
j = a.high
while j >= d:
a[j] = a[j - d]
dec(j)
j = min(d, a.len)
for i in 0 ..< j:
a[i] = h
elif d < 0: # left shift
j = -d
while j < a.len:
a[j + d] = a[j]
inc(j)
j = max(a.len + d, 0)
for i in j .. a.high:
a[i] = h
var ta = [1,1,1]
shift(ta, 1)
assert(ta == [0,1,1])
ta = [1,1,1]
shift(ta, 2)
assert(ta == [0,0,1])
ta = [1,1,1]
shift(ta, 3)
assert(ta == [0,0,0])
ta = [1,1,1]
shift(ta, 4)
assert(ta == [0,0,0])
ta = [1,1,1]
shift(ta, -1)
assert(ta == [1,1,0])
ta = [1,1,1]
shift(ta, -2)
assert(ta == [1,0,0])
ta = [1,1,1]
shift(ta, -3)
assert(ta == [0,0,0])
ta = [1,1,1]
shift(ta, -4)
assert(ta == [0,0,0])
```
