Doc::Perlish::Writer - base class for stream output functions

 # using - generally use a subclass
 my $writer = Doc::Perlish::Writer::XML->new();

 $doc->receiver($writer);
 $doc->send_all();

 my $output = $writer->output;  # an IO::All object

 # or, you can pass an object or specify an IO::All source
 $writer->output("filename");
 $writer->output(\$scalar);

 # to get the document body
 $writer->doc;

A writer is something that takes Doc::Perlish Serial API events, and converts them into a stream.