Breaking

• These changes were originally announced in release 2.7.0 (#308).
• Lwt_engine.libev now has an optional argument for selecting the libev back end (#269, #294, Jeremy Yallop).
• Lwt_io.establish_server has been changed to make it more difficult to leak file descriptors (#258, #260).
• Lwt_io.shutdown_server now evaluates to a promise, which completes when the listening socket's close(2) operation completes (#259).
• Lwt_unix.bind now evaluates to a promise, because the bind(2) system call can block for Unix domain sockets (#296, requested David Sheets).
• ocamlfind packages lwt.react, lwt.ssl, lwt.glib are replaced by lwt_react, lwt_ssl, lwt_glib. These have been separate OPAM packages, under those names, since 2.7.0 (#301).