Add quickselect algorithm. Quickselect is a selection algorithm to find the kth smallest element in an unordered list.

Currently the layer cannot be selected for low zoom levels.

It would be useful if a missing property in the config file fell back gracefully to the default value, rather than killing the process with a hard error.

Is there any appetite for such a change? We could potentially specify default values in a json file that the C++ code reads at compile time and the python script valhalla_build_config parses at runtime?