Use categories as a scoring function

[hkrishna]

Each point has a field called category that contains some valuable information, it would be nice to use this information in the scoring algorithm.

We could have a file weighted_categories.yml where we can define what weight each tag value corresponds to.

   airport: 12
   railway: 10
   restaurant: 8
   tourism: 11
   poi:landmark: 10
   ...

This should be a query time boosting easily do-able by just adding a script and using it in the API sorting logic.

Related to pelias/openstreetmap#33 and pelias/pelias#50