Support for CURL proxy

[sdiama]

Suggestion: I think, it will be a great addition if you add support for CURL requests through proxy, passed as parameter to fetch()

Reason: Sometimes, URL access is blocked or is slow from the server's country/location. In that case it's easier to setup/use a proxy server instead of creating a custom php solution from scratch.

[shweshi]

@sdiama hey.. this is a great idea and will be a valuable enhancement. Let me know if you want to take this up and create a PR for the same. Any help you need I will be happy to provide.