Controller: improved handling of unix domain control socket.

One of the ways to detect Unit's startup and subsequent readiness to accept
commands relies on waiting for the control socket file to be

Controller: improved handling of unix domain control socket.

One of the ways to detect Unit's startup and subsequent readiness to accept
commands relies on waiting for the control socket file to be created.
Earlier, it was unreliable due to a race condition between the client's
connect() and the daemon's listen() calls after the socket's bind() call.

Now, unix domain listening sockets are created with a nxt_listen_socket_create()
call as follows:

s = socket();
unlink("path/to/socket.tmp")
bind(s, "path/to/socket.tmp");
listen(s);
rename("path/to/socket.tmp", "path/to/socket");

This eliminates a time-lapse when the socket file is already created but nobody
is listening on it yet, which therefore prevents the condition described above.

Also, it allows reliably detecting whether the socket is being used or simply
wasn't cleaned after the daemon stopped abruptly. A successful connection to
the socket file means the daemon has been started; otherwise, the file can be
overwritten.

show more ...

Removed unused code related to testing of address binding.

Added SSL/TLS support on connection level.

Router: fixed segfault after configuration change.

Fixed textual socket name lengths and Unix domain sockaddr length.

Removed unused function.

Router: processing JSON configuration.

Using new memory pool implementation.

Skeleton of router configuration and request processing.

I/O operations refactoring.

Initial version.