Add new type that can be parametrized.

This commit adds new type: "int64" that can be used by
(*Graph).ParameterizedQuery method. According to the
"Cypher Coverage" section from RedisGraph documentation:
64-bit signed integer is supported literal type.

This change will allow, for example, to use time.Now().Unix()
as parameter for previously mentioned ParameterizedQuery.

Before this change, using int64 as parameter for ParameterizedQuery
result with panic, although using int64 is very common when writing
go code.

client_test.go

@@ -420,10 +420,13 @@ func TestUtils(t *testing.T) {
 	res = ToString(true)
 	assert.Equal(t, res, "true")
 
-	var arr = []interface{}{1,2,3,"boom"}
+	res = ToString(int64(10))
+	assert.Equal(t, res, "10")
+
+	var arr = []interface{}{1, 2, 3, int64(4), "boom"}
 	res = ToString(arr)
-	assert.Equal(t, res, "[1,2,3,\"boom\"]")
-	
+	assert.Equal(t, res, "[1,2,3,4,\"boom\"]")
+
 	jsonMap := make(map[string]interface{})
 	jsonMap["object"] = map[string]interface{} {"foo": 1}
 	res = ToString(jsonMap)

utils.go

@@ -48,6 +48,8 @@ func ToString(i interface{}) string {
 		return strconv.Quote(s)
 	case int:
 		return strconv.Itoa(i.(int))
+	case int64:
+		return strconv.FormatInt(i.(int64), 10)
 	case float64:
 		return strconv.FormatFloat(i.(float64), 'f', -1, 64)
 	case bool: