Give traceur.js a trim.

This removes a lot of properties from the traceur object. We used
to export everything onto it and then we stopped doing that. This
removes almost everything but the properties used from src/node.
chore(Makefile): make test-promise filter more strict + update docs

Make the promise test suite filter that skips invalid tests more strict to prevent
accidental test exclusion.

Also add a better explanation of why the sloppy (non-strict mode) tests are being skipped.
Merge pull request #930 from IgorMinar/aplus-promise-fix

chore(Makefile): make test-promise filter more strict + update docs
Merge pull request #923 from arv/cleanup-traceur-properties

Give traceur.js a trim.
Destructuring: The initializer must be an object.

The following should throw a TypeError:

```js
var {x} = 1;
```

since `1` is not an Object.

This is done by wrapping the initializer in a runtime call, called
`$traceurRuntime.assertObject`

Fixes #839
Merge pull request #927 from arv/destructuring-assert-object

Destructuring: The initializer must be an object.
Add PureES6Transformer

Add "outputLanguage" option to the Node.js API.
By the default, it's set to "es5".
When set to "es6", the PureES6Transformer will be used.