Relax City and Country database checks

The strict database checks broke the per-continent City databases,
and adding all of those to an array is a bit much (and slow).

Closes #23.

bin/benchmark.php

@@ -0,0 +1,26 @@
+#!/usr/bin/env php
+
+<?php
+
+require_once '../vendor/autoload.php';
+
+use GeoIp2\Database\Reader;
+use GeoIp2\Exception\AddressNotFoundException;
+
+$reader = new Reader('GeoLite2-City.mmdb');
+$count = 40000;
+$startTime = microtime(true);
+for ($i = 0; $i < $count; $i++) {
+    $ip = long2ip(rand(0, pow(2, 32) -1));
+    try {
+        $t = $reader->city($ip);
+    } catch (AddressNotFoundException $e) {
+    }
+    if ($i % 1000 == 0) {
+        print($i . ' ' . $ip . "\n");
+    }
+}
+$endTime = microtime(true);
+
+$duration = $endTime - $startTime;
+print('Requests per second: ' . $count / $duration . "\n");