Additions

• Implement Lwt_unix.readv and Lwt_unix.writev on Windows using Lwt_unix.read and Lwt_unix.write (#745, requested Ulrik Strid).
• Implement Lwt_unix.wait4 on Android using Unix.waitpid, as on Windows (#752, @EduardoRFS).
• LWT_DISCOVER_ARGUMENTS=--verbose flag, passed through environment variable, for debugging the feature discovery (configuration) process (#740).

Bugs fixed

• To help with fork, don't call back into Lwt_main at process exit to call Lwt exit hooks when there are none (#737, prompted Martin Jambon).
• Properly retain references to buffers in Lwt_unix.readv, Lwt_unix.writev, Lwt_bytes.read, Lwt_bytes.write, and Lwt_bytes.mincore; the references could be released too early in rare circumstances (#742, prompted Olaf Hering).
• Don't install a SIGCHLD handler when Lwt is linked in but not used (#738, requested Sam Goldman, additional information Waleed Khan).
• Link with -lpthread on more platforms that support and require the flag (#748, Olivier Andrieu).
• Fix syntax errors in feature test programs (#748, Olivier Andrieu).
• C warning with OCaml 4.10 (#751, @kit-ty-kate).

Miscellaneous

• Make tests more reliable (#726, #743, prompted Olaf Hering).
• Fix deprecation annotation on internal API (#735, Antonio Nuno Monteiro).
• Fix broken link in Lwt_mvar docs (#739, reported @tg-x).
• Fix broken links in README (#750, @imbsky).