title: How to filter tokens from spaCy document
body: <p>I would like to parse a document using spaCy and apply a token filter so that the final spaCy document does not include the filtered tokens. I know that I can take the sequence of tokens filtered, but I am insterested in having the actual <code>Doc</code> structure.  </p>
  
  <pre><code>text = u"This document is only an example. " \
      "I would like to create a custom pipeline that will remove specific tokesn from the final document."
  
  doc = nlp(text)
  
  def keep_token(tok):
      # This is only an example rule
      return tok.pos_ not not in {'PUNCT', 'NUM', 'SYM'}
  
  final_tokens = list(filter(keep_token, doc))
  
  # How to get a spacy.Doc from final_tokens?
  </code></pre>
  
  <p>I tried to reconstruct a new spaCy <code>Doc</code> from the tokens lists but the API is not clear how to do it.</p>