Simplify by using mocha's tap reporter

Advantages:

  * Smaller, simpler code
  * Human readable by default
  * Easy to pipe into other tap tools and reporters like `tap-{spec,nyan}` etc

Here's what it looks like now:

```bash
$ mocha-broken
1..3
not ok 1 GET /track/dl/:id 200 on proper req
  Error: expected 500 "Internal Server Error", got 302 "Moved Temporarily"
  
not ok 2 something timed out
  Error: timeout of 2000ms exceeded
    at [object Object].<anonymous> (/Users/jb55/dev/mocha-broken/node_modules/mocha/lib/runnable.js:139:19)
    at Timer.listOnTimeout [as ontimeout] (timers.js:110:15)
  
# tests 2
# pass 0
# fail 2
```

Piping to a reporter:

```bash
$ mocha-broken | tap-spec
```

Let me know what you think