Add support for YAML::PP(::LibYAML)

[perlpunk]

It will load only objects with the specified classes.
Note that load_file/dump_file work for filehandles too.

Also enable $LoadBlessed for YAML::XS/Syck/.pm because they were set to false by default.

For demo I added

    # only for testing
 #    $yaml_module = 'YAML::PP';
 #    $yaml_module = 'YAML::PP::LibYAML';

in _yaml_module.

[perlpunk]

Maybe it should be configurable if loading objects should be enabled or not, similar to yaml_load_code.