* redirects to a different host
* - proxyhost: string, proxy host in "host[:port]" format
* - proxyport: int, use another proxy port as specified in proxyhost
+ * - proxytype: int, HTTP_PROXY_HTTP, SOCKS4 or SOCKS5
* - proxyauth: string, proxy credentials in "user:pass" format
* - proxyauthtype: int, HTTP_AUTH_BASIC and/or HTTP_AUTH_NTLM
* - httpauth: string, http credentials in "user:pass" format
* - cookiesession: bool, accept (true) or reset (false) sessioncookies
* - resume: int, byte offset to start the download from;
* if the server supports ranges
+ * - range: array, array of arrays, each containing two integers,
+ * specifying the ranges to download if server support is
+ * given; only recognized if the resume option is empty
* - maxfilesize: int, maximum file size that should be downloaded;
* has no effect, if the size of the requested entity is not known
* - lastmodified: int, timestamp for If-(Un)Modified-Since header