Add option to update TLDs list over proxy

[czechnology]

I am in a scenario where the Internet can only be accessed over a proxy, yet that proxy is not meant to be in env. vars.
This PR adds option to update the TLDs over a proxy, without unnecessarily cluttering the main class initializer with proxies.

[floer32]

First reaction was - hmm I wish we did not have to cascade this argument through a number of places. But I do agree it's ideal not to have it in the constructor. Just wondering if at this point, should it support passing in a Session instance instead of this one argument?

@john-kurkowski thoughts?

[john-kurkowski]

I agree @hangtwenty. Let's not maintain our own requests shim language, always playing catchup. Let the caller optionally decide how we should make requests, with whatever requests options they want.

[floer32]

@czechnology Support the overall idea but if we are opening it up to customization let's really open it up. Could you change it to support customization by passing Session? this will allow the proxy use case (but probably won't even mention the proxy argument specifically in the code now, as it's a requests detail, not us).

ignore snippet I just deleted, I meant to delete that before posting (realized that part was wrong)

[john-kurkowski]

Closing due to inactivity. Concentrate on #158.