sleepy_penguin 3.5.1

This release fixes some minor things for kqueue and clang
users.  Not much going on... *yawn*

6 changes since v3.5.0 (2017-03-22):

      kqueue: ensure close-on-exec flag is set
      kqueue: modernize Struct usage for Ruby 2.5.0dev
      fix 64-to-32-bit truncation warning
      kqueue: get rid of unused variable warnings
      epoll: avoid reduce block capture and ivar requests
      doc: use HTTPS URLS when possible