Add searchIndex method to list the available searchIndexs per location

I created a bitmask map of the [SearchIndexValues table](http://docs.amazonwebservices.com/AWSECommerceService/latest/DG/APPNDX_SearchIndexValues.html) and a function to return the available values for a given location.

I'm not super excited 120 character width of the bitmask map, and am open to alter formatting suggestions.