Add proxy support

[chuyume]

coz soundcloud is banned here so i can only access via shadowsocks etc. so i need proxy thanks.
Network Options:

--proxy URL Use the specified HTTP/HTTPS/SOCKS proxy.
To enable SOCKS proxy, specify a proper
scheme. For example
socks5://127.0.0.1:1080/. Pass in an empty
string (--proxy "") for direct connection
--socket-timeout SECONDS Time to wait before giving up, in seconds
--source-address IP Client-side IP address to bind to
-4, --force-ipv4 Make all connections via IPv4
-6, --force-ipv6 Make all connections via IPv6

[Rich Jones]

This is a good idea

[chuyume]

This is a good idea

glad to hear