introduce mapper package

The mapper package contains functions related to creating and marshalling
reponses to machines.

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

hscontrol/mapper/suite_test.go

@@ -0,0 +1,15 @@
+package mapper
+
+import (
+	"testing"
+
+	"gopkg.in/check.v1"
+)
+
+func Test(t *testing.T) {
+	check.TestingT(t)
+}
+
+var _ = check.Suite(&Suite{})
+
+type Suite struct{}