Initial/simple handling of Server notifications/requests

[IndianBoy42]

• log::trace more messages
• Naive handling of server requests

[IndianBoy42]

I've been using this for rust programming for the last week and it is correctly getting all my configuration and hasn't crashed otherwise. To be fair I am not really multiplexing and just using it to make restarting my editor faster.

[IndianBoy42]

Fixes #15

[Ddystopia]

Thank you for your work! It seems to work well, but there is one little issue: it does not react to the changes in editor's configuration until ra-multiplex is fully restarted and with multiple projects opened.

[IndianBoy42]

Hmm thats pretty strange, on my machine I see all the configuration messages/requests/responses going through correctly, and a simple testing with trying to change between cargo clippy and cargo check works (no restart of ra-multiplex server required, just the editor). Could you give an example where the editor configuration change doesn't apply? preferable with the logs (use RUST_LOG=trace ra-multiplex server to see all requests and responses)