Add versioner interface to wrap versioning operations

This allows to scope responsabilities and enables switching to different
ordering algorithms

pkg/versioner/interface.go

@@ -0,0 +1,25 @@
+// Copyright © 2019-2020 Ettore Di Giacinto <mudler@gentoo.org>,
+//                  Daniele Rondina <geaaru@sabayonlinux.org>
+//
+// This program is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 2 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this program; if not, see <http://www.gnu.org/licenses/>.
+
+package version
+
+// Versioner is responsible of sanitizing versions,
+// validating them and ordering by precedence
+type Versioner interface {
+	Sanitize(string) string
+	Validate(string) error
+	Sort([]string) []string
+}