title: Elasticsearch - Autocomplete return word/term/token suggestions instead of whole documents
body: <p>I am trying to implement a simple auto completion for query terms.
  There are many different approaches but most of them do return documents instead of terms
  - or the authors simply stopped explaining from that point and i am  not able to adapt.</p>
  
  <p>A user is typing in a query - e.g. <em>phil</em>
  What i want is to <strong>provide a list of term completion suggestions</strong> like <em>philipp, philius, philadelphia, ...</em></p>
  
  <p>I am able to get document matches via (edge)ngrams, phrase_prefix and so on but i am am stuck at retrieving matching terms (completion suggestions).</p>
  
  <p>Can someone give me a hint?</p>
  
  <p>I have documents like this {"title":"...", "description":"...", "content":"..."}
  All fields have larger string values but especially the field content contains fulltext content.</p>
  
  <p>I do not want to suggest the whole title of a document containing e.g. Philadelphia. Just the word "Philadelphia".</p>