[#199] owner: Rename to user, refactor and doc

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

user/util_test.go

@@ -0,0 +1,24 @@
+package user_test
+
+import (
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"encoding/hex"
+	"testing"
+
+	"github.com/nspcc-dev/neofs-sdk-go/user"
+	"github.com/stretchr/testify/require"
+)
+
+func TestIDFromKey(t *testing.T) {
+	// examples are taken from https://docs.neo.org/docs/en-us/basic/concept/wallets.html
+	rawPub, _ := hex.DecodeString("03cdb067d930fd5adaa6c68545016044aaddec64ba39e548250eaea551172e535c")
+	x, y := elliptic.UnmarshalCompressed(elliptic.P256(), rawPub)
+	require.True(t, x != nil && y != nil)
+
+	var id user.ID
+
+	user.IDFromKey(&id, ecdsa.PublicKey{Curve: elliptic.P256(), X: x, Y: y})
+
+	require.Equal(t, "NNLi44dJNXtDNSBkofB48aTVYtb1zZrNEs", id.EncodeToString())
+}