refactor: use a common logger for consistency

All kapow messages will end up in stderr (incl. debug mode).
stdout is reserved for the access logs.

Co-authored-by: Roberto Abdelkader Martínez Pérez <robertomartinezp@gmail.com>

internal/logger/logger.go

@@ -0,0 +1,12 @@
+package logger
+
+import (
+	"log"
+	"os"
+)
+
+var L *log.Logger
+
+func init() {
+	L = log.New(os.Stderr, "", log.LstdFlags|log.Lmicroseconds|log.LUTC)
+}