Add not equal comparator (!=)

The `qb.Cmp` lacks `not equal` methods related to the operator `!=`
even though the documentation
https://docs.scylladb.com/getting-started/dml/#select-statement mentions
it.

Closes: #114

Signed-off-by: Pierangelo Di Pilato <pierangelodipilato@gmail.com>

qb/cmp_test.go

@@ -103,6 +103,16 @@ func TestCmp(t *testing.T) {
 			S: "like LIKE (?,?)",
 			N: []string{"like_0", "like_1"},
 		},
+		{
+			C: Ne("ne"),
+			S: "ne!=?",
+			N: []string{"ne"},
+		},
+		{
+			C: NeTuple("ne", 3),
+			S: "ne!=(?,?,?)",
+			N: []string{"ne_0", "ne_1", "ne_2"},
+		},
 
 		// Custom bind names
 		{
@@ -145,6 +155,11 @@ func TestCmp(t *testing.T) {
 			S: "cntKey CONTAINS KEY ?",
 			N: []string{"name"},
 		},
+		{
+			C: NeNamed("ne", "name"),
+			S: "ne!=?",
+			N: []string{"name"},
+		},
 
 		// Literals
 		{
@@ -175,6 +190,10 @@ func TestCmp(t *testing.T) {
 			C: ContainsLit("cnt", "litval"),
 			S: "cnt CONTAINS litval",
 		},
+		{
+			C: NeLit("ne", "litval"),
+			S: "ne!=litval",
+		},
 
 		// Functions
 		{
@@ -214,6 +233,11 @@ func TestCmp(t *testing.T) {
 			S: "eq>=maxTimeuuid(?)",
 			N: []string{"arg0"},
 		},
+		{
+			C: NeFunc("ne", Fn("fn", "arg0", "arg1", "arg2")),
+			S: "ne!=fn(?,?,?)",
+			N: []string{"arg0", "arg1", "arg2"},
+		},
 	}
 
 	buf := bytes.Buffer{}