Change underscore import/export boiler plate

Fixes #186

Lets you do

```js
var _ = require("underscore-contrib/underscore.object.selectors");
```

PS I would also like to remove the `underscore.*` prefixes
Works with https://github.com/megawac/ros-backbone/blob/_-c-te/package.json#L24 with 6->5. I think its good