Add automatic rules to manage version number

Former-commit-id: f4fcc1927f4169025c1d8cc88c5f3abcdc76037c

pkg/obioptions/version.go

@@ -0,0 +1,16 @@
+package obioptions
+
+import (
+	"fmt"
+)
+
+var _Commit = ""
+var _Version = "Release 4.2.0"
+
+// Version returns the version of the obitools package.
+//
+// No parameters.
+// Returns a string representing the version of the obitools package.
+func VersionString() string {
+	return fmt.Sprintf("%s (%s)", _Version, _Commit)
+}