Added exception for aliased beers and checks for situations where ratings may not be available

Implemented the changes to deal with examples such as these:

  * [3 Fonteinen Akkurat’s Oude Geuze 50/50](http://www.ratebeer.com/beer/3-fonteinen-akkurats-oude-geuze-50-50/34145/) (an aliased beer)
  * [3 Fonteinen Kriekenlambik Schaerbeekse Version](http://www.ratebeer.com/beer/3-fonteinen-kriekenlambik-schaerbeekse-version/141086/) (No rating currently available)