This also adds support for both the v1 and v2 APIs to set the Proxy
function on the underlying http.Transport.
The functionality for proxy environment variables is provided by the
[http.ProxyFromEnvironment](https://godoc.org/net/http#ProxyFromEnvironment).
The string `node <n>` can be used to specify which data node the data
should be retrieved from. This uses the `node_id=X` query parameter that
is supported, but wasn't exposed anywhere in the client library.
We use this feature enough internally when attempting to find
inconsistencies or network errors that it is easier if this is just
supported. Otherwise, I continue having to recompile the CLI program
every time I need to do this.
To clear a previously set node, you can use `node 0` or `node clear`.