[#231] object: Implement string encode/decode methods on Type

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

v2/object/string.go

@@ -0,0 +1,29 @@
+package object
+
+const (
+	typeRegularString      = "Regular"
+	typeTombstoneString    = "Tombstone"
+	typeStorageGroupString = "StorageGroup"
+)
+
+func (t Type) String() string {
+	switch t {
+	default:
+		return typeRegularString
+	case TypeTombstone:
+		return typeTombstoneString
+	case TypeStorageGroup:
+		return typeStorageGroupString
+	}
+}
+
+func TypeFromString(s string) Type {
+	switch s {
+	default:
+		return TypeRegular
+	case typeTombstoneString:
+		return TypeTombstone
+	case typeStorageGroupString:
+		return TypeStorageGroup
+	}
+}