typeahead: allow multiple line expression

This PR will allow developers to use newlines in the typeahead string, giving them the chance to improve the readability of their code

Example:
```
    <input ng-model="selected"
           typeahead="datum as datum.name for datum in data
                        | filter:{name: $viewValue}
                        | orderBy: datum.name"
           typeahead-on-select="goToElement($item)">
```