title: YAML 1.2 directive with multiple files doesn't work in unsafe mode
body: <p>I'm trying to load a multi-file yaml config file like the following:</p>
  
  <p>file:</p>
  
  <pre><code>%YAML 1.2
  ---
  num_epochs: 1
  ---
  num_epochs: 1
  </code></pre>
  
  <p>and the python script is:</p>
  
  <pre><code>from ruamel.yaml import YAML
  
  yaml = YAML(typ='unsafe')
  configs = yaml.load_all(Path(Experiment.config_file))
  for config in configs:
      print(config)
  </code></pre>
  
  <p>when executed, it gives the following error:</p>
  
  <pre><code>ruamel.yaml.parser.ParserError: found incompatible YAML document
  in "../MAML_tensorflow/experiment.yml", line 1, column 1
  </code></pre>
  
  <p>The file works if I use <code>load_all</code> directly import from the module. Is this expected behavior?</p>
  
  <p>This is likely a bug, because setting the implementation flag to <code>pure</code> gives the correct parse result.</p>
  
  <pre><code>from ruamel.yaml import YAML
  
  yaml = YAML(typ='unsafe', pure=True)
  configs = yaml.load_all(Path(Experiment.config_file))
  for config in configs:
  print(config)
  </code></pre>
  
  <p>while this does not and gives the error above</p>
  
  <pre><code>from ruamel.yaml import YAML
  
  yaml = YAML(typ='unsafe')
  configs = yaml.load_all(Path(Experiment.config_file))
  for config in configs:
      print(config)
  </code></pre>