versioning: plugins report a list of supported versions

Further progress on versioning support (Issue #266).
Bump CNI spec version to 0.3.0

plugins/main/macvlan/macvlan.go

@@ -26,6 +26,7 @@ import (
 	"github.com/containernetworking/cni/pkg/skel"
 	"github.com/containernetworking/cni/pkg/types"
 	"github.com/containernetworking/cni/pkg/utils/sysctl"
+	"github.com/containernetworking/cni/pkg/version"
 	"github.com/vishvananda/netlink"
 )
 
@@ -193,5 +194,5 @@ func renameLink(curName, newName string) error {
 }
 
 func main() {
-	skel.PluginMain(cmdAdd, cmdDel)
+	skel.PluginMain(cmdAdd, cmdDel, version.Legacy)
 }