Add helper functions to the feedback package for CLI output

The log is used for output during the sync process, but that format is not necessary when the tool is being used directly
by a maintainer.

These functions will ensure that all the warning and error output displayed during manual processes has a consistent
format.

Author: per1234

internal/feedback/feedback.go

@@ -25,7 +25,9 @@
 package feedback
 
 import (
+	"fmt"
 	"log"
+	"os"
 )
 
 // LogError logs non-nil errors and returns whether the error was nil.
@@ -36,3 +38,25 @@ func LogError(err error) bool {
 	}
 	return false
 }
+
+// Warningf behaves like fmt.Printf but adds a prefix and newline.
+func Warningf(format string, v ...interface{}) {
+	Warning(fmt.Sprintf(format, v...))
+}
+
+// Warning behaves like fmt.Println but adds a prefix.
+func Warning(v ...interface{}) {
+	fmt.Fprint(os.Stderr, "warning: ")
+	fmt.Fprintln(os.Stderr, v...)
+}
+
+// Errorf behaves like fmt.Printf but adds a prefix and newline.
+func Errorf(format string, v ...interface{}) {
+	Error(fmt.Sprintf(format, v...))
+}
+
+// Error behaves like fmt.Println but adds a prefix.
+func Error(v ...interface{}) {
+	fmt.Fprint(os.Stderr, "error: ")
+	fmt.Fprintln(os.Stderr, v...)
+}