Can't know FtCLI random assigned port

[pinaf]

When running FtCLI with --port=0, the socket is opened on a random port, as expected, but there is no way to know which port was actually allocated.

Let's add a method int port() that informs this.

[davvd]

@yegor256 dispatch this issue please, see par.21

[yegor256]

@pinaf this is by design. if you want to know the port number, you should do something like this:

--port=/tmp/port.txt

This file will be created and will contain the port number.

[yegor256]

@pinaf I should probably add this to class documentation...

[yegor256]

@pinaf documented in 57b1fb9

[pinaf]

@yegor256 thank you.