title: Create custom token filter with NEST
body: <p>How can I configure Index using NEST with such JSON:</p>
  
  <pre><code>"settings":{
    "analysis":{
       "filter":{
          "name_ngrams":{
             "side":"front",
             "max_gram":50,
             "min_gram":2,
             "type":"edgeNGram"
          }
       },
       "analyzer":{            
          "partial_name":{
             "filter":[
                "standard",
                "lowercase",
                "asciifolding",
                "name_ngrams"
             ],
             "type":"custom",
             "tokenizer":"standard"
          }
       }
    }
  </code></pre>
  
  <p>I could create my custom analyzer using <code>CustomAnalyzer</code> class, but I could'n find how to create custom filter and register it within my analyzer. </p>
  
  <p>Thanks in advance!</p>