feat: add configuration through file

A file named `config.toml` can now be used to load the address, port,
and some websocket configuration settings.

Fixes https://todo.sr.ht/~gheartsfield/nostr-rs-relay/3

src/lib.rs

@@ -1,4 +1,5 @@
 pub mod close;
+pub mod config;
 pub mod conn;
 pub mod db;
 pub mod error;