non-printable characters are not supported inside quoted scalars

YAML standard [section 5.1](http://www.yaml.org/spec/1.2/spec.html#id2770814) explicitly allows non-printables in quoted scalars for JSON compatibility, `js-yaml` doesn't:

```
> require('js-yaml').load('"\ud800"')
JS-YAML: the stream contains non-printable characters at line 1, column 1:
    "���"
    ^
```

```
> JSON.parse('"\ud800"')
'���'
```
