Add support for proxy parameters in Connection.new()

[dineshnamburi]

This is an enhancement request.

net-http2 gem supports proxy parameters (proxy host, port, user, password).
So, it would be great if we can pass these parameters in Apnotic::Connection.new() which in turn creates net-http2 client with these proxy params.
It will be useful for Apnotic gem users, working behind a corporate proxy.

Thanks!

[n-miyo]

Hi @ostinelli, thank you for creating good gem!

Do you have a plan to create code for solving this issue? I created a small PR #78 for supporting proxy settings. Could you check it if you have time.
Thank you.