Added ch 16 soutions

Ripped from the chapter:

<pre>unless (system 'date') {
# Return was zero, meaning success
print "We gave you a date, OK!\n";
}
Note that this is backward from the normal “true is good—false is bad” strategy for
most of the operators, so to write a typical “do this or die” style, we’ll need to flip false
and true. The easiest way is to simply prefix the system operator with a bang (the logicalnot
operator):
!system 'rm -rf files_to_delete' or die 'something went wrong';</pre>