add sort support to search, add index fields command, fix error messages (#25)

cmd/search.go

@@ -100,6 +100,19 @@ func Search(conf *cfg.Config) *cli.Command {
 				Destination: &conf.TimestampFormat,
 				Value:       "strict_date_hour_minute",
 			},
+			&cli.StringFlag{
+				Name:        "sort-by",
+				Usage:       "sort by a field",
+				Destination: &conf.SortBy,
+				Value:       "@timestamp",
+				Aliases:     []string{"k"},
+			},
+			&cli.BoolFlag{
+				Name:        "ascending",
+				Usage:       "sort in ascending order (default: descending)",
+				Destination: &conf.Ascending,
+				Aliases:     []string{"a"},
+			},
 			&cli.BoolFlag{
 				Name:        "help-jsonpath",
 				Usage:       "show jsonPath help",