Use arrays for slightly better caching in indieauth-client-php

Client.php

<?php
namespace IndieAuth;
use BarnabyWalters\Mf2;

class Client {

  private static $_headers = array(); //if you bump requirement to php5.4 we could use short syntax
  private static $_body = array();
  
  //skip some code

  private static function _fetchHead($url) {
    if(array_key_exists($url, self::$_headers)) {
      return self::$_headers[$url];
  } else {
      $ch = curl_init($url);
      self::_setUserAgent($ch);
      curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
      curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
      curl_setopt($ch, CURLOPT_HEADER, true);
      curl_setopt($ch, CURLOPT_NOBODY, true);
      self::$_headers[$url] = curl_exec($ch);
      return self::$_headers[$url];
    }
  }

  private static function _fetchBody($url) {
    if(array_key_exists($host, self::$_body)) {
      return self::$_body[$url];
  } else {
      $ch = curl_init($url);
      self::_setUserAgent($ch);
      curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
      curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
      self::$_body[$url] = curl_exec($ch);
      return self::$_body[$url];
    }
  }