Improve error handling (#33)

* refactor: improve error handling

* fix: specify bind address instead of port

* fix: remove temporary testing file

* fix(errors): change error names to snake_case

* refactor(errors): split indexing error types, remove unused errors

* feat: add env variable checking at program start

This just checks whether the enviroment variables exist and can
parse to the given type and gives a warning if they can't. This
should prevent cases where the program fails at runtime due to
checking an environment variable that doesn't exist.

src/database/mongo_database.rs

@@ -6,7 +6,8 @@ use mongodb::Client;
 pub async fn connect() -> Result<Client, Error> {
     info!("Initializing database connection");
 
-    let mut client_options = ClientOptions::parse(&dotenv::var("MONGODB_ADDR").unwrap()).await?;
+    let mongodb_addr = dotenv::var("MONGODB_ADDR").expect("`MONGO_ADDR` not in .env");
+    let mut client_options = ClientOptions::parse(&mongodb_addr).await?;
     client_options.app_name = Some("labrinth".to_string());
 
     Client::with_options(client_options)