`Client` URL cannot be modified

[tcharding]

bitcoind adds the wallet to the URL for a bunch of API calls (eg getnewaddress) for example:

http://localhost:1234/wallet/<wallet-name>

However it is not possible to modify a Client's url (inside Transport), it would be sweet if when implementing an RPC client usingjsonrpc one could do something like

let client = Client::new();
let wallet = client.create_wallet()?;
let wallet_client = client.use_wallet(&wallet);
let address = wallet_client.get_new_address()?;
// Original client still usable
let another_wallet = client.some_other_non_wallet_api_call()?;