Add support for GZIP encoding

[cbortz]

The Vainglory API allows for requesting compressed responses if desired, so we should support that. The plan is to leave it disabled by default. When instantiating a new VaingloryAPI::Client a user should be able to pass in the option to enable it. For example:

VaingloryAPI.new("API_KEY", "na", gzip: true)

Additional information: https://developer.vainglorygame.com/docs#gzip

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As a side note...

After looking at the previous example, I think I want to start accepting a single options parameter as a hash when instantiating new clients. The updated syntax might look like this:

VaingloryAPI.new("API_KEY", region: "na", gzip: true)

If I do implement this change, I should allow for backward compatibility because I am nowhere near ready to bump to v1.

[cbortz]

Closing this because Net::HTTP does this for us automatically.