Pushing changes for testing harness before my next meeting. Adding working exec library and sample code

Signed-off-by: Kris Nóva <kris@nivenly.com>

examples/common.go

@@ -0,0 +1,30 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	photoprism "github.com/kris-nova/client-go"
+
+	"github.com/kris-nova/logger"
+)
+
+// format string, a ...interface{}
+func halt(code int, msg string, a ...interface{}) {
+	str := fmt.Sprintf(msg, a...)
+	logger.Critical(str)
+	os.Exit(code)
+}
+
+func auth() photoprism.ClientAuthenticator {
+	user := os.Getenv("PHOTOPRISM_USER")
+	if user == "" {
+		halt(1, "Missing PHOTOPRISM_USER")
+	}
+	pass := os.Getenv("PHOTOPRISM_PASS")
+	if pass == "" {
+		halt(2, "Missing PHOTOPRISM_PASS")
+	}
+	auth := photoprism.NewClientAuthLogin(user, pass)
+	return auth
+}