Proxy support via Curl

[mikemn]

Hello,

I wrote a patch to add proxy support via Curl. I wanted to consolidate my private backend multiple servers through a proxy gateway when connecting to an external validation server.

Command line usage: --proxy=socks5h://user:pass@10.10.0.1:1080
Adds libykclient function: ykclient_set_proxy

Valid Curl schemes are: socks4://, socks4a://, socks5:// or socks5h:// (the last one to enable socks5 and asking the proxy to do the dns resolving). If no scheme or port is specified HTTP proxy port 1080 will be used per Curl defaults.

If this is a good proposal I also have a patch ready to go for Yubico/yubico-pam.

Pull request to follow. Thanks.

[mikemn]

These were both merged. Thanks!