New json document mapping for docs

With issue #38 closed (replace mapper-attachment-plugin by Tika), we can now cleanup the JSON structure we generate when indexing documents with FSRiver.

In 0.3.0 version, the JSon mapping is the following:

```javascript
{
  "doc" : {
    "properties" : {
      "file" : {
        "type" : "attachment",
        "path" : "full",
        "fields" : {
          "file" : {
            "type" : "string",
            "store" : "yes",
            "term_vector" : "with_positions_offsets"
          },
          "author" : {
            "type" : "string"
          },
          "title" : {
            "type" : "string",
            "store" : "yes"
          },
          "name" : {
            "type" : "string"
          },
          "date" : {
            "type" : "date",
            "format" : "dateOptionalTime"
          },
          "keywords" : {
            "type" : "string"
          },
          "content_type" : {
            "type" : "string",
            "store" : "yes"
          }
        }
      },
      "name" : {
        "type" : "string",
        "analyzer" : "keyword"
      },
      "pathEncoded" : {
        "type" : "string",
        "analyzer" : "keyword"
      },
      "postDate" : {
        "type" : "date",
        "format" : "dateOptionalTime"
      },
      "rootpath" : {
        "type" : "string",
        "analyzer" : "keyword"
      },
      "virtualpath" : {
        "type" : "string",
        "analyzer" : "keyword"
      },
      "filesize" : {
        "type" : "long"
      }
    }
  }
}
```

We can see that we have different levels of metadata and some of them are redundant.
Also, we use `keyword` analyzer instead of not indexing at all fields or using no analyzer.

The new structure will be:

```javascript
{
  "doc" : {
    "properties" : {
      "content" : {
        "type" : "string",
        "store" : "yes"
      },
      "meta" : {
        "properties" : {
          "author" : {
              "type" : "string",
              "store" : "yes"
          },
          "title" : {
              "type" : "string",
              "store" : "yes"
          },
          "date" : {
              "type" : "date",
              "format" : "dateOptionalTime",
              "store" : "yes"
          },
          "keywords" : {
              "type" : "string",
              "store" : "yes"
          }
        }
      },
      "file" : {
        "properties" : {
          "content_type" : {
              "type" : "string",
              "analyzer" : "simple",
              "store" : "yes"
          },
          "last_modified" : {
              "type" : "date",
              "format" : "dateOptionalTime",
              "store" : "yes"
          },
          "indexing_date" : {
              "type" : "date",
              "format" : "dateOptionalTime",
              "store" : "yes"
          },
          "filesize" : {
              "type" : "long",
              "store" : "yes"
          },
          "indexed_chars" : {
              "type" : "long",
              "store" : "yes"
          },
          "filename" : {
              "type" : "string",
              "analyzer" : "simple",
              "store" : "yes"
          },
          "url" : {
              "type" : "string",
              "store" : "yes",
              "index" : "no"
          }
        }
      },
      "path" : {
        "properties" : {
          "encoded" : {
              "type" : "string",
              "store" : "yes",
              "index" : "not_analyzed"
          },
          "virtual" : {
              "type" : "string",
              "store" : "yes",
              "index" : "not_analyzed"
          },
          "root" : {
              "type" : "string",
              "store" : "yes",
              "index" : "not_analyzed"
          },
          "real" : {
              "type" : "string",
              "store" : "yes",
              "index" : "not_analyzed"
          }
        }
      }
    }
  }
}
```

Closes #39.