Location based API used as the basis of a reminder app.
POST /contacts -- add contact to a users contact list
request: {id: user_id, contacts: [ contact1, contact2, ... ]}
POST /ping -- update user location
request: {id: user_id, location: {lat: lat, lon: lon, alt: altitude}}
POST /near -- get nearby contacts
request: {id: user_id, location: {lat: lat, lon: lon, alt: altitude}}
response: [ contact1, contact2, ... ]