feat: updated dataset (20201013)

This updates the IPv4 City geoip dataset to the latest version
provided on https://dev.maxmind.com/geoip/geoip2/geolite2/

The b-tree format and lookup logic remain unchanged, however the code
responsible for building the b-tree had to be changed to work with the
new CSV format of the source dataset.

Closes #68
Closes #63

BREAKING CHANGE: `area_code` and `metro_code` are no longer provided due to upstream changes

License: MIT
Signed-off-by: Marcin Rataj <[email protected]>

README.md

@@ -70,8 +70,6 @@ Returns a promise that resolves to an object of the form
   "postal_code": "94040",
   "latitude": 37.3860,
   "longitude": -122.0838,
-  "metro_code": "807",
-  "area_code": "650",
   "planet": "Earth"
 }
 ```
@@ -85,6 +83,11 @@ a `formatted` property that looks like this: `Mountain View, CA, United States,
 
 The utility geoip-gen reads csv files provided from GeoLite, and turns them into a 32-way branching b-tree, which is stored as ipfs json objects.
 
+**Note:** this library uses old type of ipfs json objects for legacy reasons,
+be mindful of that and do not use its code as an example.  Modern code should
+use [`dag-cbor`](https://github.com/ipld/specs/blob/master/block-layer/codecs/dag-cbor.md)
+and [`ipfs.dag`](https://github.com/ipfs/js-ipfs/blob/master/docs/core-api/DAG.md) API.
+
 There is a generator included, that can be run with
 
 ```bash
@@ -107,8 +110,6 @@ Result: {
   "postal_code": "94040",
   "latitude": 37.386,
   "longitude": -122.0838,
-  "metro_code": "807",
-  "area_code": "650",
   "planet": "Earth"
 }
 Pretty result: Mountain View, CA, USA, Earth
@@ -130,4 +131,6 @@ This repository falls under the IPFS [Code of Conduct](https://github.com/ipfs/c
 
 ## License
 
-[MIT](LICENSE)
+ipfs-geoip is [MIT](LICENSE) licensed.
+
+This library includes GeoLite2 data created by MaxMind, available from [maxmind.com](http://www.maxmind.com).