update changes

MIGRATION.md

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+## Migration from 0.5 to 0.6
+
+* `ws::Message::Close` now includes optional close reason.
+  `ws::CloseCode::Status` and `ws::CloseCode::Empty` have been removed.
+
+
+## Migration from 0.4 to 0.5
+
+* `HttpResponseBuilder::body()`, `.finish()`, `.json()`
+   methods return `HttpResponse` instead of `Result<HttpResponse>`
+
+* `actix_web::Method`, `actix_web::StatusCode`, `actix_web::Version`
+   moved to `actix_web::http` module
+
+* `actix_web::header` moved to `actix_web::http::header`
+
+* `NormalizePath` moved to `actix_web::http` module
+
+* `HttpServer` moved to `actix_web::server`, added new `actix_web::server::new()` function,
+  shortcut for `actix_web::server::HttpServer::new()`
+
+* `DefaultHeaders` middleware does not use separate builder, all builder methods moved to type itself
+
+* `StaticFiles::new()`'s show_index parameter removed, use `show_files_listing()` method instead.
+
+* `CookieSessionBackendBuilder` removed, all methods moved to `CookieSessionBackend` type
+
+* `actix_web::httpcodes` module is deprecated, `HttpResponse::Ok()`, `HttpResponse::Found()` and other `HttpResponse::XXX()`
+   functions should be used instead
+
+* `ClientRequestBuilder::body()` returns `Result<_, actix_web::Error>`
+  instead of `Result<_, http::Error>`
+
+* `Application` renamed to a `App`
+
+* `actix_web::Reply`, `actix_web::Resource` moved to `actix_web::dev`