Add v2 version to go module name

Replace all elements from `v2` to root directory.

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

refs/json.go

@@ -0,0 +1,62 @@
+package refs
+
+import (
+	refs "github.com/nspcc-dev/neofs-api-go/v2/refs/grpc"
+	"github.com/nspcc-dev/neofs-api-go/v2/rpc/message"
+)
+
+func (a *Address) MarshalJSON() ([]byte, error) {
+	return message.MarshalJSON(a)
+}
+
+func (a *Address) UnmarshalJSON(data []byte) error {
+	return message.UnmarshalJSON(a, data, new(refs.Address))
+}
+
+func (o *ObjectID) MarshalJSON() ([]byte, error) {
+	return message.MarshalJSON(o)
+}
+
+func (o *ObjectID) UnmarshalJSON(data []byte) error {
+	return message.UnmarshalJSON(o, data, new(refs.ObjectID))
+}
+
+func (c *ContainerID) MarshalJSON() ([]byte, error) {
+	return message.MarshalJSON(c)
+}
+
+func (c *ContainerID) UnmarshalJSON(data []byte) error {
+	return message.UnmarshalJSON(c, data, new(refs.ContainerID))
+}
+
+func (o *OwnerID) MarshalJSON() ([]byte, error) {
+	return message.MarshalJSON(o)
+}
+
+func (o *OwnerID) UnmarshalJSON(data []byte) error {
+	return message.UnmarshalJSON(o, data, new(refs.OwnerID))
+}
+
+func (v *Version) MarshalJSON() ([]byte, error) {
+	return message.MarshalJSON(v)
+}
+
+func (v *Version) UnmarshalJSON(data []byte) error {
+	return message.UnmarshalJSON(v, data, new(refs.Version))
+}
+
+func (s *Signature) MarshalJSON() ([]byte, error) {
+	return message.MarshalJSON(s)
+}
+
+func (s *Signature) UnmarshalJSON(data []byte) error {
+	return message.UnmarshalJSON(s, data, new(refs.Signature))
+}
+
+func (c *Checksum) MarshalJSON() ([]byte, error) {
+	return message.MarshalJSON(c)
+}
+
+func (c *Checksum) UnmarshalJSON(data []byte) error {
+	return message.UnmarshalJSON(c, data, new(refs.Checksum))
+}