[feature] latitude and longitude should not have to be exact to match a location

[akhoury]

The lat and long are now used as keys, so the input values MUST exactly match.

Current behavior:

// this matches

zipdb.latlong("42.71", "-71.18");
/* { zipcode: '01844',
  type: 'standard',
  city: 'Methuen',
  state: 'MA',
  latitude: '42.71',
  longitude: '-71.18' }
*/

// but those do not, even though they are either a little off or have more decimal points

zipdb.latlong("42.711", "-71.18");
// {}

zipdb.latlong("42.72", "-71.18");
// {}

zipdb.latlong("42.71", "-71.14");
// {}

// you get the gist

It would be nice if you can build a matrix and when you dont get a hit, you return the closest zipcode.