Bump version to 4.1.0 and write changelog

[skip ci]

CHANGES

@@ -1,3 +1,23 @@
+===== 4.1.0 (2018-06-26) =====
+
+====== Additions ======
+
+  * Change license to MIT (#560).
+  * Lwt_fmt, an Lwt-aware version of Format (#548, Gabriel Radanne).
+  * Lwt_io.establish_server_with_client_socket (#586).
+
+====== Bugs fixed ======
+
+  * Lwt_stream.iter_n: rename ?max_threads argument to ?max_concurrency (#581,
+    Hezekiah Carty).
+  * PPX: reject match expressions that have only exception cases (#597, Raphaël
+    Proust).
+
+====== Miscellaneous ======
+
+  * Improvements to Lwt_pool docs (#575, Bobby Priambodo).
+  * Restore all PPX tests (#590, Jess Smith).
+
 ===== 4.0.1 (2018-04-13) =====
 
 ====== Bugs fixed ======

README.md

@@ -1,6 +1,6 @@
-# Lwt    [![version 4.0.1][version]][releases] [![Gitter chat][gitter-img]][gitter] [![Travis status][travis-img]][travis] [![AppVeyor status][appveyor-img]][appveyor]
+# Lwt    [![version 4.1.0][version]][releases] [![Gitter chat][gitter-img]][gitter] [![Travis status][travis-img]][travis] [![AppVeyor status][appveyor-img]][appveyor]
 
-[version]:      https://img.shields.io/badge/version-4.0.1-blue.svg
+[version]:      https://img.shields.io/badge/version-4.1.0-blue.svg
 [releases]:     https://github.com/ocsigen/lwt/releases
 [gitter-img]:   https://img.shields.io/badge/chat-on_gitter-lightgrey.svg
 [travis]:       https://travis-ci.org/ocsigen/lwt/branches