v2.4.0

• Fix: avoid segfaults when kqueue descriptors are cleaned up.

• Fix: Prevent potential dead-lock in linux_kqueue_init()

• Fix: slight deadlock in thread_start()

• Fix: missing inotify_rm_watch()

• Fix: call close() in an error handling path

• Fix: take the write lock when freeing knotes

• Keep a separate state tree for file descriptors inserted into epoll to avoid conflicts between
  EVFILT_READ and EVFILT_WRITE (Closes #29 Closes #59)

• Fix: deadlock and memory leak in kqueue()

• Fix: use after free issue in decrementing kq reference counts

• Default to marking file descriptors as passive sockets if fstat() doesn't hint at the type
  (Closes #97)

• Fix various leaks and issues found by LSAN

• Install event.h in $INCLUDEDIR/kqueue/sys, rather than $INCLUDEDIR/sys

• Add support for building native Debian packages using Docker

• Detect raw sockets.

• Use high-resolution wait on Linux for timeouts finer than a millisecond.

• Various CMake improvements.