yahns 1.18.0

8 changes since 1.17.0 (2019-04-22):

      worker: workaround old F_SETPIPE_SZ bug
      doc: favor File.read over IO.read to ease review
      proxy_pass: document as a public API
      doc: include Yahns/ directory on website
      extras/try_gzip_static: set "Vary: Accept-Encoding" on gzip
      do not sleep if signals are pending
      server: workaround Linux v5.5..v5.13 epoll bug
      gemspec: allow unicorn 6.x