[#3] Call #close properly when exception in Display::Screen#initialize .

When an exception occurred in `Display::Screen#initialize`, `#close` did
not get called, meaning Curses-related cleanup did not occur. Fix by
rescuing as part of `#initialize`, calling `#close`, and reraising.

This enables error messages to be output to the screen; otherwise,
nothing shows because of failure to shutdown Curses-related things.
[#3] Report executable errors friendily unless --debug .

If errors are raised within the application, rescue and report in a
friendly manner. An example of this is if the host cannot be reached.
Also return a non-zero exit status. Introduce `--debug` option, for
reraising so the stacktrace is reported.