provide an interface to access generated output more as a stream

i'd have to actually try it but it'll be something along
```perl
sub yum_error {
    my ($self, $line) = @_;
    if ($line =~/error/i) {
         # do something
        $self->error("a line with error in it: $line");
    }
}
my $p = CAF::Process->new([qw(yum install package)]);
my $allout = $p->stream_output(\&yum_error, mode => 'line', arguments => [$self]);
```
i'm not sure what you mean with `croak`, this is a running process after all. e.g. if you'd send the kill signal, you have to be sure that yum deals with that (eg no corrupt rpmdb and all that).