use roaring conventions for variable names

Roaring likes to call things "a" and "b", not "1" and "2",
and use "n" for length, not "l", etcetera. Adopt these
conventions to make code more readable.

Also drop the 'vb' value since it isn't expensive to
compute and the compiler can figure out that it can
reuse the value.

roaring/roaring.go

@@ -1903,25 +1903,24 @@ func intersectionCount(a, b *Container) int32 {
 
 func intersectionCountArrayArray(a, b *Container) (n int32) {
 	statsHit("intersectionCount/ArrayArray")
-	s1, s2 := a.array, b.array
-	if len(s1) == 0 || len(s2) == 0 {
+	ca, cb := a.array, b.array
+	na, nb := len(ca), len(cb)
+	if na == 0 || nb == 0 {
 		return 0
 	}
-	if len(s1) > len(s2) {
-		s1, s2 = s2, s1
+	if na > nb {
+		ca, cb = cb, ca
+		na, nb = nb, na
 	}
-	l2 := len(s2)
-	i2 := 0
-	v2 := s2[0]
-	for _, v1 := range s1 {
-		for v2 < v1 {
-			i2++
-			if i2 >= l2 {
+	j := 0
+	for _, va := range ca {
+		for cb[j] < va {
+			j++
+			if j >= nb {
 				return n
 			}
-			v2 = s2[i2]
 		}
-		if v2 == v1 {
+		if cb[j] == va {
 			n++
 		}
 	}