pkg: hide it by moving to _pkg.dev

The idea here is to preserve the history of `dev` branch development and its
code when merging with the `master`. Later this code could be moved into the
masters code where appropriate.

_pkg.dev/wire/payload/mgetdata.go

@@ -0,0 +1,18 @@
+package payload
+
+import (
+	"github.com/CityOfZion/neo-go/pkg/wire/command"
+)
+
+// GetDataMessage represents a GetData message on the neo-network
+type GetDataMessage struct {
+	*InvMessage
+}
+
+//NewGetDataMessage returns a GetDataMessage object
+func NewGetDataMessage(typ InvType) (*GetDataMessage, error) {
+	getData, err := newAbstractInv(typ, command.GetData)
+	return &GetDataMessage{
+		getData,
+	}, err
+}