Add Coinbase account balance example

examples/coinbase_account_balance.php

@@ -0,0 +1,22 @@
+<?php
+require '../src/Curl.class.php';
+
+
+define('API_KEY', '');
+define('API_SECRET', '');
+
+$url = 'https://coinbase.com/api/v1/account/balance';
+
+$nonce = (int)(microtime(true) * 1e6);
+$message = $nonce . $url;
+$signature = hash_hmac('sha256', $message, API_SECRET);
+
+$curl = new Curl();
+$curl->setHeader('ACCESS_KEY', API_KEY);
+$curl->setHeader('ACCESS_SIGNATURE', $signature);
+$curl->setHeader('ACCESS_NONCE', $nonce);
+$curl->get($url);
+
+echo
+    'My current account balance at Coinbase is ' .
+    $curl->response->amount . ' ' . $curl->response->currency . '.' . "\n";