Catching up with:

* Mocha, which has had these as part of its suites since
  mochajs/mocha@c0bb9188 (plugging in Hook, 2011-11-25), and

* Mochawesome, which has expected arrays since at least
  adamgruber/mochawesome@5a49d410 (3.0, 2017-11-30,
  adamgruber/mochawesome#214).

Without this change, Mochawesome's:

  [].concat(suite._beforeAll, suite._beforeEach)

will lead to:

  [undefined, undefined]

and Mochawesome will call cleanTest on those undefined values and
crash.

Catching up with mochajs/mocha@30582e64 (if a reporter has a .done
method, call it before exiting, 2014-05-17, mochajs/mocha#1218).

Mochawesome has used:

  skipped = (!cleaned.pass && !cleaned.fail && !cleaned.pending);

since adamgruber/mochawesome@2d4a63b7 (logic to record skipped tests,
2015-01-29).

Do not emit 'test end' for skips or TODO (pending) tests, because
Mochawesome has:

  obj.stats.skipped = obj.stats.testsRegistered - obj.stats.tests;

since that same commit, so we need these tests entered in
testsRegistered (via the 'test' event) but not in tests (via the 'test
end' event).

Do not emit 'pass' for skips either, otherwise we'll end up with
failures + passes > tests.

Also fix "pass" -> "passed" for .state.  Mochawesome has been
comparing the value to "passed" in its cleaner since
adamgruber/mochawesome@d687633d (Initial commit, 2014-07-11), and
Mocha itself has been comparing with "passed" since at least
mochajs/mocha@2c720a35 (do not eat exceptions thrown asynchronously
from passed tests, 2018-02-28, mochajs/mocha#3257).

This is, as far as I know, Mochawesome-specific, which makes it a bit
of a hack.  The Mochawesome side of this is
adamgruber/mochawesome@65e90621 (implement addContext method for
adding report context to tests, 2016-12-20,
adamgruber/mochawesome#106).  Ideally we'd want a way to trigger this
as part of requesting Mochawesome as the reporter, but the addition
seems harmless enough so I'm just including it every time.

In the diag.source case, we might want to expose diagnostics besides
.fn.  But we surely don't want to expose the test source via both .fn
and .context.  For this commit, I've left the diag.source case alone,
but in future work we might want something closer to :

  if (result.diag) {
    var context = Object.assign({}, result.diag)
    if (context.source) {
      var source = context.source
      delete context.source
      this.fn = {
        toString: function () {
          return 'function(){' + source + '\n}'
        }
      }
    }
    if (Object.keys(context).length) {
      this.context = {
        title: 'diagnostic',
        value: context,
      }
    }
  }

I haven't done that here, because Object.assign is not supported on
Internet Exporer, Android webview, or Opera for Android [1], despite
being part of ECMAScript 2015 [2].  Object.keys seems to be supported
everywhere [3].  We may only care about Node for this package, but I'm
being conservative for this commit.

[1]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign#Browser_compatibility
[2]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign#Specifications
[3]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys#Browser_compatibility

Skips like [1]:

  ok 23 # skip Insufficient flogiston pressure.

are parsed (at least by [email protected]) into structures like:

  {
    id: 1,
    name: "",
    ok: true,
    skip: "root.readonly is false but the root filesystem is still not writable"
  }

But title-less tests are not very useful.  With this change, cases
like the above empty-string name will fall back to the skip value.
And if that skip value is undefined, we'll fall back to an empty
string (because I'm not sure how well downstream consumers would
handle and undefined title).

One positive effect of this change is that Mochawesome now has a title
message to render for these skips (where previously it just used an
empty h4).

[1]: https://testanything.org/tap-version-13-specification.html#skipping-tests

Mochawesome has expected a suite attached to the runner since
adamgruber/mochawesome@e25a5eb0 (handle nested describes, 2014-07-14).
This commit creates a new root Suite for that, and attaches the
per-TAP suites as children of the root suite.  This will allow us to
render output from multiple TAP files with Mochawesome.

I've also refactored the ancestory properties:

* Test.parent became Test.suite, since that's the only object type
  we're using there.

* Suite.parent now only references other Suites.  There's no need to
  complicate the ancestry by including both Suites and Parsers, and
  sticking to suites means we don't need Parser methods for title
  chaining.

The new titlePath methods catch us up with mochajs/mocha@aa24e82f
(indent test contexts, 2017-05-20, mochajs/mocha#2814).  I've left
fullTitle around for now for compat with older versions of Mocha.

This allows us to use reporters that aren't built in.  For example,
with this commit you can:

  $ npm install
  $ npm install --no-save mocha mochawesome
  $ cp index.js node_modules/tap-mocha-reporter/
  $ cp lib/*.js node_modules/tap-mocha-reporter/lib/
  $ npm test -- --reporter=mochawesome

That's installing [email protected] and [email protected].