Add state param to users/by_location

[rickr]

Feature

Why is this feature being added?

We should be able to get a count of users in a specific state. Right now it looks like all searches are done by a radius from a point.

What should your feature do?

Add a new param to the users/by_location action called state. It should perform a query on the users table and return a count of the users in a particular state.
Make sure to update teh docs

This is blocked by #105