Added iterface for Reader/Client.

It could use a better name.

src/GeoIp2/Database/Reader.php

@@ -7,6 +7,7 @@ use GeoIp2\Model\City;
 use GeoIp2\Model\CityIspOrg;
 use GeoIp2\Model\Country;
 use GeoIp2\Model\Omni;
+use GeoIp2\ProviderInterface;
 use MaxMind\Db\Reader as DbReader;
 
 /**
@@ -38,7 +39,7 @@ use MaxMind\Db\Reader as DbReader;
  * will be thrown.
  *
  */
-class Reader
+class Reader implements ProviderInterface
 {
     private $dbReader;
     private $languages;

src/GeoIp2/ProviderInterface.php

@@ -0,0 +1,34 @@
+<?php
+
+namespace GeoIp2;
+
+interface ProviderInterface
+{
+    /**
+     * @param ipAddress
+     *            IPv4 or IPv6 address to lookup.
+     * @return A Country model for the requested IP address.
+     */
+    public function country($ipAddress);
+
+    /**
+     * @param ipAddress
+     *            IPv4 or IPv6 address to lookup.
+     * @return A City model for the requested IP address.
+     */
+    public function city($ipAddress);
+
+    /**
+     * @param ipAddress
+     *            IPv4 or IPv6 address to lookup.
+     * @return A CityIspOrg model for the requested IP address.
+     */
+    public function cityIspOrg($ipAddress);
+
+    /**
+     * @param ipAddress
+     *            IPv4 or IPv6 address to lookup.
+     * @return An Omni model for the requested IP address.
+     */
+    public function omni($ipAddress);
+}

src/GeoIp2/WebService/Client.php

@@ -12,6 +12,7 @@ use GeoIp2\Model\City;
 use GeoIp2\Model\CityIspOrg;
 use GeoIp2\Model\Country;
 use GeoIp2\Model\Omni;
+use GeoIp2\ProviderInterface;
 use Guzzle\Http\Client as GuzzleClient;
 use Guzzle\Common\Exception\RuntimeException;
 use Guzzle\Http\Exception\ClientErrorResponseException;
@@ -48,7 +49,7 @@ use Guzzle\Http\Exception\ServerErrorResponseException;
  *
  * If the request fails, the client class throws an exception.
  */
-class Client
+class Client implements ProviderInterface
 {
     private $userId;
     private $licenseKey;