Made all unnecessary output "verbose"

Silence is a virtue.

Now the program only outputs the diagnostic messages when "--verbose" is
set.
Added "network-cat.exe" to ".gitignore"

When I use CygWin (G++ on Windows) it generates "network-cat.exe", even
if I don't specify ".exe"
Added "--colors" option, don't show colors by default

By default it doesn't print things with color anymore.
Requires user to force with "--colors".

That's to avoid messing stuff up when redirecting to files.