title: Elasticsearch "starts with" first word in phrases
body: <p>I try to implement an A - Z navigation for my content with Elasticsearch. 
  What I need, is displaying all results which begins with e.g. a,b,c,... etc.</p>
  
  <p>I've tried:</p>
  
  <pre><code>"query": {
          "match_phrase_prefix" : {
          "title" : {
              "query" : "a"
          }
        }
      }
  </code></pre>
  
  <p>The query mentioned above also display results, where within the string a word begins with a. 
  Example:</p>
  
  <p>"title": "Apfelpfannkuchen",</p>
  
  <p>"title": "Affogato",</p>
  
  <p>"title": "Kalbsschnitzel <strong>a</strong>n <strong>A</strong>ceto Balsamico",</p>
  
  <p>I want to display only phrase where the FIRST word begins with a.</p>
  
  <p>Here the mapping I use:</p>
  
  <pre><code>$params = array(
              'index' =&gt; 'my_index',
              'body' =&gt; array(
                  'settings' =&gt; array(
                      'number_of_shards' =&gt; 1,
                      'index' =&gt; array(
                          'analysis' =&gt; array(
                              'filter' =&gt; array(
                                  'nGram_filter' =&gt; array(
                                      'type' =&gt; 'nGram',
                                      'min_gram' =&gt; 2,
                                      'max_gram' =&gt; 20,
                                      'token_chars' =&gt; array('letter', 'digit', 'punctuation', 'symbol')
                                  )
                              ),
                              'analyzer' =&gt; array(
                                  'nGram_analyzer' =&gt; array(
                                      'type' =&gt; 'custom',
                                      'tokenizer' =&gt; 'whitespace',
                                      'filter' =&gt; array('lowercase', 'asciifolding', 'nGram_filter')
                                  ),
                                  'whitespace_analyzer' =&gt; array(
                                      'type' =&gt; 'custom',
                                      'tokenizer' =&gt; 'whitespace',
                                      'filter' =&gt; array('lowercase', 'asciifolding')
                                  ),
                                  'analyzer_startswith' =&gt; array(
                                      'tokenizer' =&gt; 'keyword',
                                      'filter' =&gt; 'lowercase'
                                  )
                              )
                          )
                      )
                  ),
                  'mappings' =&gt; array(
                      'tags' =&gt; array(
                          '_all' =&gt; array(
                              'type' =&gt; 'string',
                              'index_analyzer' =&gt; 'nGram_analyzer',
                              'search_analyzer' =&gt; 'whitespace_analyzer'
                          ),
                          'properties' =&gt; array()
  
                      ),
                      'posts' =&gt; array(
                          '_all' =&gt; array(
                              'index_analyzer' =&gt; 'nGram_analyzer',
                              'search_analyzer' =&gt; 'whitespace_analyzer'
                          ),
                          'properties' =&gt; array(
                              'title' =&gt; array(
                                  'type' =&gt; 'string',
                                  'index_analyzer' =&gt; 'analyzer_startswith',
                                  'search_analyzer' =&gt; 'analyzer_startswith'
                              )
                          )
                      )
                  )
              )
          );
  </code></pre>