Added a few changes to query expressions (#51)

- Added the between operator to query expressions.
- Added the using query expression suffix to specify which index to query (or force a scan). This is required if query planning has found multiple indices that can potentially be used.
- Rewrote the types of the query expressions to allow for functions to be defined once, and be useful in queries that result in DynamoDB queries, and evaluation.
- Added some test functions around time and summing numbers.
- Fixed a bug in the del-attr which was not honouring marked rows in a similar way to set-attr: it was only deleting attributes from the first row.
- Added the -to type flag to set-attr which will set the attribute to the value of a query expression.

test/cmd/load-test-table/main.go

@@ -91,10 +91,14 @@ func main() {
 		}
 	}
 
-	key := gofakeit.UUID()
+	var key = gofakeit.UUID()
 	for i := 0; i < totalItems; i++ {
+		if i%50 == 0 {
+			key = gofakeit.UUID()
+		}
 		if err := tableService.Put(ctx, inventoryTableInfo, models.Item{
 			"pk":   &types.AttributeValueMemberS{Value: key},
+			"sk":   &types.AttributeValueMemberN{Value: fmt.Sprint(i % 50)},
 			"uuid": &types.AttributeValueMemberS{Value: gofakeit.UUID()},
 		}); err != nil {
 			log.Fatalln(err)