Update to elasticsearch 1.1.1 / Lucene 4.7.2

Related to #61.
Fix typo for JSON fields
Add highlighting documentation

Closes #54.
Setting "_content_type" in indexing request has no effect

Example below. I set the type as text/plain but it is identified as text/html.

```sh
#!/bin/sh

echo "\n\n Delete testidx \n"
curl -XDELETE "http://localhost:9200/testidx"

echo "\n\n Create index and mapping \n"
curl -XPUT "http://localhost:9200/testidx" -d'
{
  "mappings": {
    "session": {
      "properties": {
        "Content": {
          "properties": {
            "content": {
              "type": "attachment",
              "path": "full",
              "store": "yes",
              "fields": {
                "content": {
                  "type": "string",
                  "store": "yes"
                },
                "author": {
                  "type": "string",
                  "store": "yes"
                },
                "title": {
                  "type": "string",
                  "store": "yes"
                },
                "name": {
                  "type": "string",
                  "store": "yes"
                },
                "date": {
                  "type": "date",
                  "format": "dateOptionalTime",
                  "store": "yes"
                },
                "keywords": {
                  "type": "string",
                  "store": "yes"
                },
                "content_type": {
                  "type": "string",
                  "store": "yes"
                },
                "content_length": {
                  "type": "integer",
                  "store": "yes"
                }
              }
            }
          }
        }
      }
    }
  }
}'

echo "\n\n Index document \n"
curl -XPOST "http://localhost:9200/_bulk" -d'
  {"index":{"_index":"testidx","_type":"session"}}
  {"Content":[{"_content_type":"text/plain","content":"BASE64ENCODED_CONTENT"}]}
'

echo "\n\n Refresh \n"
curl -XPOST "http://localhost:9200/testidx/_refresh"

echo "\n\n Get doc type \n"
curl -XPOST "http://localhost:9200/testidx/_search?pretty" -d'
{
  "fields": ["Content.content.content_type","Content.content.content_length","Content.content"]
}'
```

Closes #65.