[#44] version: move package from neofs-api-go

Also remove `Version` from constructors and rename `SDKVersion` to
`Current`.

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

version/version_test.go

@@ -0,0 +1,90 @@
+package version
+
+import (
+	"testing"
+
+	"github.com/nspcc-dev/neofs-api-go/v2/refs"
+	"github.com/stretchr/testify/require"
+)
+
+func TestNewVersion(t *testing.T) {
+	t.Run("default values", func(t *testing.T) {
+		v := New()
+
+		// check initial values
+		require.Zero(t, v.Major())
+		require.Zero(t, v.Minor())
+
+		// convert to v2 message
+		vV2 := v.ToV2()
+
+		require.Empty(t, vV2.GetMajor())
+		require.Empty(t, vV2.GetMinor())
+	})
+
+	t.Run("setting values", func(t *testing.T) {
+		v := New()
+
+		var mjr, mnr uint32 = 1, 2
+
+		v.SetMajor(mjr)
+		v.SetMinor(mnr)
+
+		require.Equal(t, mjr, v.Major())
+		require.Equal(t, mnr, v.Minor())
+
+		ver := v.ToV2()
+
+		require.Equal(t, mjr, ver.GetMajor())
+		require.Equal(t, mnr, ver.GetMinor())
+	})
+}
+
+func TestSDKVersion(t *testing.T) {
+	v := Current()
+
+	require.Equal(t, uint32(sdkMjr), v.Major())
+	require.Equal(t, uint32(sdkMnr), v.Minor())
+}
+
+func TestVersionEncoding(t *testing.T) {
+	v := New()
+	v.SetMajor(1)
+	v.SetMinor(2)
+
+	t.Run("binary", func(t *testing.T) {
+		data, err := v.Marshal()
+		require.NoError(t, err)
+
+		v2 := New()
+		require.NoError(t, v2.Unmarshal(data))
+
+		require.Equal(t, v, v2)
+	})
+
+	t.Run("json", func(t *testing.T) {
+		data, err := v.MarshalJSON()
+		require.NoError(t, err)
+
+		v2 := New()
+		require.NoError(t, v2.UnmarshalJSON(data))
+
+		require.Equal(t, v, v2)
+	})
+}
+
+func TestNewVersionFromV2(t *testing.T) {
+	t.Run("from nil", func(t *testing.T) {
+		var x *refs.Version
+
+		require.Nil(t, NewFromV2(x))
+	})
+}
+
+func TestVersion_ToV2(t *testing.T) {
+	t.Run("nil", func(t *testing.T) {
+		var x *Version
+
+		require.Nil(t, x.ToV2())
+	})
+}