Use strings for mapping types instead of keywords

The getting started page was referring to mappings via a keyword when creating a document. When this happens a separate mapping is created (and used):

```
{
  "myapp2_development" : {
    "person" : {
      "properties" : {
        "age" : {
          "type" : "integer"
        },
        "biography" : {
          "type" : "string",
          "term_vector" : "with_positions_offsets",
          "analyzer" : "snowball"
        },
        "first-name" : {
          "type" : "string",
          "store" : true
        },
        "last-name" : {
          "type" : "string"
        },
        "planet" : {
          "type" : "string"
        },
        "title" : {
          "type" : "string",
          "analyzer" : "snowball"
        },
        "username" : {
          "type" : "string",
          "store" : true
        }
      }
    },
    ":person" : {
      "properties" : {
        "age" : {
          "type" : "long"
        },
        "biography" : {
          "type" : "string"
        },
        "first-name" : {
          "type" : "string"
        },
        "last-name" : {
          "type" : "string"
        },
        "planet" : {
          "type" : "string"
        },
        "title" : {
          "type" : "string"
        },
        "username" : {
          "type" : "string"
        }
      }
    }
  }
}
```