add support for paths wrapped in single-quotes along with tests

Wanted to get the ball rolling on supporting wrapped paths, as discussed in #178 and requested in https://github.com/mikeric/rivets/issues/178#issuecomment-27847371

Wrapped paths are useful when the path passed to the adapter contains characters that could be misinterpreted as an adapter, such as backbone deep model.

```
<div>{ model:'sub.prop' }</div>

model.get('sub.prop') // should be this
model.get('sub').prop // not this
model.get("'sub")["prop'"] // nor this
```

The implementation is fairly flexible. We can use different wrapping delimeters (allow user to define it?). Using a regex to parse also opens the door to supporting multi-char adapters (e.g. `->`).