Add cookie convenience funcs

Fix test helper func

libkiwi_test.go

@@ -58,7 +58,7 @@ func TestGetPost(t *testing.T) {
 	t.Logf("Post text: %s\n", post.TextContent())
 }
 
-func newTestKF() (*KF, error) {
+func newTestKF() (KF, error) {
 	host := os.Getenv("TEST_HOST")
 	if host == "" {
 		host = _TEST_HOST
@@ -66,7 +66,7 @@ func newTestKF() (*KF, error) {
 
 	u, err := url.Parse("https://" + host)
 	if err != nil {
-		return nil, err
+		return KF{}, err
 	}
 
 	p := proxy.FromEnvironment()
@@ -76,7 +76,7 @@ func newTestKF() (*KF, error) {
 
 	jar, err := cookiejar.New(nil)
 	if err != nil {
-		return nil, err
+		return KF{}, err
 	}
 
 	hc := http.Client{