to generate a trusted root certificate, an intermediate certificate, and a server certificate.
We use `certificateAuthority(int)` to create certificates that can sign other certificates. The
int specifies how many intermediate certificates are allowed beneath it in the chain.

```java
HeldCertificate rootCertificate = new HeldCertificate.Builder()
    .certificateAuthority(1)

Here's a complete example:

```java
public void test() throws Exception {
  // Create a MockWebServer. These are lean enough that you can create a new
  // instance for every unit test.
  MockWebServer server = new MockWebServer();

  // Schedule some responses.
  server.enqueue(new MockResponse().setBody("hello, world!"));
  server.enqueue(new MockResponse().setBody("sup, bra?"));

implementation.  The HPACK test cases are in a separate git submodule, so to
initialize them, you must run:

    git submodule init
    git submodule update

TODO
----

 * Add maven goal to avoid manual call to git submodule init.
 * Make hpack-test-case update itself from git, and run new tests.
 * Add maven goal to generate stories and a pull request to hpack-test-case