api: Add go files

I know this is a huge commit, but I can't be bothered to check
this in part by part.

api/domain_update_test.go

@@ -0,0 +1,27 @@
+package main
+
+import (
+	"testing"
+)
+
+func TestDomainUpdateBasics(t *testing.T) {
+	failTestOnError(t, setupTestEnv())
+
+	domainNew("temp-owner-hex", "Example", "example.com")
+
+	d, _ := domainList("temp-owner-hex")
+
+	d[0].Name = "Example2"
+
+	if err := domainUpdate(d[0]); err != nil {
+		t.Errorf("unexpected error updating domain: %v", err)
+		return
+	}
+
+	d, _ = domainList("temp-owner-hex")
+
+	if d[0].Name != "Example2" {
+		t.Errorf("expected name=Example2 got name=%s", d[0].Name)
+		return
+	}
+}