adopt actix-settings crate (#270)

* adopt actix-settings crate

* add licenses and readme addition

* revamp readme

* delete temp prettier file

actix-settings/examples/actix.rs

@@ -0,0 +1,82 @@
+use actix_settings::{ApplySettings as _, Mode, Settings};
+use actix_web::{
+    get,
+    middleware::{Compress, Condition, Logger},
+    web, App, HttpServer, Responder,
+};
+
+#[get("/")]
+async fn index(settings: web::Data<Settings>) -> impl Responder {
+    format!(
+        r#"{{
+  "mode": "{}",
+  "hosts": ["{}"]
+}}"#,
+        match settings.actix.mode {
+            Mode::Development => "development",
+            Mode::Production => "production",
+        },
+        settings
+            .actix
+            .hosts
+            .iter()
+            .map(|addr| { format!("{}:{}", addr.host, addr.port) })
+            .collect::<Vec<_>>()
+            .join(", "),
+    )
+    .customize()
+    .insert_header(("content-type", "application/json"))
+}
+
+#[actix_web::main]
+async fn main() -> std::io::Result<()> {
+    let mut settings = Settings::parse_toml("./examples/Server.toml")
+        .expect("Failed to parse `Settings` from Server.toml");
+
+    // If the environment variable `$APPLICATION__HOSTS` is set,
+    // have its value override the `settings.actix.hosts` setting:
+    Settings::override_field_with_env_var(&mut settings.actix.hosts, "APPLICATION__HOSTS")?;
+
+    init_logger(&settings);
+
+    HttpServer::new({
+        // clone settings into each worker thread
+        let settings = settings.clone();
+
+        move || {
+            App::new()
+                // Include this `.wrap()` call for compression settings to take effect:
+                .wrap(Condition::new(
+                    settings.actix.enable_compression,
+                    Compress::default(),
+                ))
+                .wrap(Logger::default())
+                // make `Settings` available to handlers
+                .app_data(web::Data::new(settings.clone()))
+                .service(index)
+        }
+    })
+    // apply the `Settings` to Actix Web's `HttpServer`
+    .apply_settings(&settings)
+    .run()
+    .await
+}
+
+/// Initialize the logging infrastructure
+fn init_logger(settings: &Settings) {
+    if !settings.actix.enable_log {
+        return;
+    }
+
+    std::env::set_var(
+        "RUST_LOG",
+        match settings.actix.mode {
+            Mode::Development => "actix_web=debug",
+            Mode::Production => "actix_web=info",
+        },
+    );
+
+    std::env::set_var("RUST_BACKTRACE", "1");
+
+    env_logger::init();
+}