Use interfaces, add unit tests, add duration diff support (#3)

* use interface for Duration and Time printing, fix diff ts parsing
* add unit tests and gpl
* added tests, add support for duration diff+add
* bump version
* catch setenv errors
* fix ci job name

cmd/root.go

@@ -1,10 +1,25 @@
+/*
+Copyright © 2025 Thomas von Dein
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program. If not, see <http://www.gnu.org/licenses/>.
+*/
+
 package cmd
 
 import (
-	"fmt"
 	"io"
 	"log"
-	"os"
 )
 
 func Die(err error) int {
@@ -19,14 +34,6 @@ func Main(output io.Writer) int {
 		return Die(err)
 	}
 
-	if conf.Examples {
-		_, err := fmt.Fprintln(output, Examples)
-		if err != nil {
-			Die(err)
-		}
-		os.Exit(0)
-	}
-
 	tp := NewTP(conf)
 
 	if err := tp.ProcessTimestamps(); err != nil {