refactor(mlablocate*): move from i/e/internal to internal (#385)

We've been flattening the package structure for some time now.

While there, add very basic examples.

internal/mlablocate/example_test.go

@@ -0,0 +1,19 @@
+package mlablocate_test
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+
+	"github.com/apex/log"
+	"github.com/ooni/probe-cli/v3/internal/mlablocate"
+)
+
+func Example_usage() {
+	clnt := mlablocate.NewClient(http.DefaultClient, log.Log, "miniooni/0.1.0-dev")
+	result, err := clnt.Query(context.Background(), "neubot/dash")
+	if err != nil {
+		log.WithError(err).Fatal("clnt.Query failed")
+	}
+	fmt.Printf("%s\n", result.FQDN)
+}