Add max_results optional arg to geocode

[robe]

By default geocode will limit to return 10 results, but you can pass in say 1 if you just want the best result back.

This will save people from having to do unnecessary distinct ons and will also speed up some queries as we can reduce number of queries to run too.

[robe]

done at r7518. Still need to do some performance enhancements to geocode_address, but that won't change the interface.