Support 'state' files using addresses

For the client/server, we need to be able to keep track of currently-loaded files as well as their version, etc. This means we should create a config that is able to be read by the client/server based on the current configuration.

E.g. $HOME/.local/share/nvim/remote/client/my-address.com.9999.json
```
:RemoteConnect my-address.com 9999
```

and

E.g. $HOME/.local/share/nvim/remote/server/my-address.com.9999.json
```
:RemoteListen my-address.com 9999
```