[Elixir]Release http_proxy support record/play request

I released http_proxy 0.3.0 which support play/record http request.

Now, the library support multiple port proxy and each proxies support play/record request.

Hex: https://hex.pm/packages/http_proxy
Docs: http://hexdocs.pm/http_proxy/0.3.0/extra-api-reference.html
GitHub: https://github.com/KazuCocoa/http_proxy