WIP rewrite the daemon

cmd subdir does not build on purpose, it's only left in tree to grab old
code and move it to github.com/zrepl/zrepl/daemon

endpoint/context.go

@@ -0,0 +1,26 @@
+package endpoint
+
+import (
+	"context"
+	"github.com/zrepl/zrepl/logger"
+)
+
+type contextKey int
+
+const (
+	contextKeyLogger contextKey = iota
+)
+
+type Logger = logger.Logger
+
+func WithLogger(ctx context.Context, log Logger) context.Context {
+	return context.WithValue(ctx, contextKeyLogger, log)
+}
+
+func getLogger(ctx context.Context) Logger {
+	l, ok := ctx.Value(contextKeyLogger).(Logger)
+	if !ok {
+		l = logger.NewNullLogger()
+	}
+	return l
+}