Simple POSIX I/O emulation layer to work around Windows's defective

Unix I/O:
[_WIN32] (socklen_t, accept, posix_accept, bind. posix_bind, listen)
(posix_listen, setsockopt, posix_setsockopt, shutdown, posix_shutdown)
(socket, posix_socket, close, posix_close, creat, fstat, posix_fstat)
(lseek, posix_lseek, open, posix_open, read, posix_read, write)
(posix_write, fileno, posix_fileno, fcntl, O_NONBLOCK, F_RDLCK)
(F_WRLCK, F_GETFL, F_SETFL, F_SETLK, EWOULDBLOCK, ENOTSOCK)
(flock, fsync, posix_fsync):
New.
(ef_open, io_close, io_input, io_output, io_shutdown, io_noblocking)
(player_accept): Use them to simplify.
[_WIN32] (posix_fd2socket): New.
(empth_select): Use it.
(gen_power): Use it.

src/lib/player/player.c

@@ -32,9 +32,7 @@
  */
 
 #include <config.h>
-#if !defined(_WIN32)
 #include <unistd.h>
-#endif
 #include <stdio.h>
 #include <errno.h>
 #include <fcntl.h>