Setup Shadowsocks Proxy for Terminal on OS X

Use privoxy to forward http proxy to socks5 proxy.

Install privoxy by using brew:
```
 $ brew install privoxy
```
Add these lines to /usr/local/etc/privoxy/config:
```
 listen-address [::1]:8118
 listen-address  127.0.0.1:8118
 forward-socks5 / localhost:1080 .
```
Note:
1. There might be already a listen-address 127.0.0.1:8118 line in the file, do not repeat it.
2. listen-address [::1]:8118 is for IPv6, it’s important because it’s required for some tools (as I known: wget).
Add these scripts to your shell profile (for bash on OS X, it’s ~/.bash_profile) for helping enable/disable proxy:

  function set_proxy_on()
  {
      /usr/local/sbin/privoxy /usr/local/etc/privoxy/config
      export http_proxy='http://localhost:8118'
      export https_proxy=$http_proxy
      export ftp_proxy=$http_proxy
      export rsync_proxy=$http_proxy
  }

  function set_proxy_off()
  {
      unset http_proxy
      unset https_proxy
      unset ftp_proxy
      unset rsync_proxy
      ps -A | grep sbin\/privoxy | grep -v grep | cut -d' ' -f2 | xargs kill -9
  }

Then reload profile:

  $ source ~/.bash_profile

Now, just run:

  $ set_proxy_on

to turn on proxy. Run:

  $ set_proxy_off

to turn off proxy.

Note: