v4.3.0-beta.1: add support for proxy

• Add support for http and socks5 proxy. Command line option --proxy and environment variable http_proxy(or HTTP_PROXY) are available.
  • Example: aspeak --proxy "socks5://127.0.0.1:7890" text "Hello World"
  • You can also set the proxy in the auth section in your profile.
  • By now, connection to https proxy server is not supported!
  • For python binding, use the proxy keyword argument in the SpeechService constructor.