Bump to 5.1.0 and write changelog

Author: aantron

CHANGES

@@ -1,3 +1,16 @@
+===== 5.1.0 (2019-12-28) =====
+
+====== Additions ======
+
+  * Lwt.all (9976f67).
+
+====== Documentation ======
+
+  * Add index.mld for nicer odoc output (1059a80, prompted Anurag Soni).
+  * Link to rwo-lwt from the online manual to make it more discoverable
+    (4129a22, suggested Anurag Soni).
+  * Fix doc links in opam files (7617607).
+
 ===== 5.0.1 (2019-12-22) =====
 
 ====== Bugs fixed ======

README.md

@@ -1,6 +1,6 @@
-# Lwt    [![version 5.0.1][version]][releases] [![Travis status][travis-img]][travis] [![AppVeyor status][appveyor-img]][appveyor]
+# Lwt    [![version 5.1.0][version]][releases] [![Travis status][travis-img]][travis] [![AppVeyor status][appveyor-img]][appveyor]
 
-[version]:      https://img.shields.io/badge/version-5.0.1-blue.svg
+[version]:      https://img.shields.io/badge/version-5.1.0-blue.svg
 [releases]:     https://github.com/ocsigen/lwt/releases
 [travis]:       https://travis-ci.org/ocsigen/lwt/branches
 [travis-img]:   https://img.shields.io/travis/ocsigen/lwt/master.svg?label=travis