Constants, comments, CI fixes, dead code clean-up (#21)

* constants

* server.rs docs

* client.rs comments

* dead code; comments

* comment

* query cancellation comments

* remove unnecessary cast

* move db setup up one step

* query cancellation test

* new line; good night

src/main.rs

@@ -35,6 +35,7 @@ use tokio::sync::mpsc;
 
 mod client;
 mod config;
+mod constants;
 mod errors;
 mod messages;
 mod pool;