Release 0.7.1

Improve expected / actual reporting
----------
- https://twitter.com/azu_re/status/466027072712753154

```
  assert(this.ary.indexOf(zero) === two)
              |   |       |     |   |
              |   |       |     |   2
              |   -1      0     false
              [1,2,3]

  [number] two
  => 2
  [number] this.ary.indexOf(zero)
  => -1
```

Throw Error at test execution time if dependencies are not found
----------
- https://twitter.com/azu_re/status/466019000816652289
- https://twitter.com/vvakame/status/466039580357976064

```
    ✘ power-assert requires google's `diff_match_patch` library since 0.7.0. Please check your dependencies.
        Error: power-assert requires google's `diff_match_patch` library since 0.7.0. Please check your dependencies.
            at http://localhost:7357/bower_components/power-assert-formatter/lib/power-assert-formatter.js:595:23
            at buildPowerAssertText (http://localhost:7357/bower_components/empower/lib/empower.js:150:35)
            at doPowerAssert (http://localhost:7357/bower_components/empower/lib/empower.js:135:37)
            at http://localhost:7357/bower_components/empower/lib/empower.js:202:20
            at powerAssert (http://localhost:7357/bower_components/empower/lib/empower.js:99:17)
            at Context.<anonymous> (http://localhost:7357/powered-test/test.js:19:27)
            at callFn (http://localhost:7357/testem/mocha.js:4338:21)
            at Test.Runnable.run (http://localhost:7357/testem/mocha.js:4331:7)
            at Runner.runTest (http://localhost:7357/testem/mocha.js:4728:10)
            at http://localhost:7357/testem/mocha.js:4806:12
```