Implement 知識Q&A

```ruby
client = Docomoru::Client.new(api_key: ENV["DOCOMO_API_KEY"])
response = client.create_knowledge("Rubyの作者は誰ですか")
response.status #=> 200
response.headers #=> {
    "Asyncserviceinvoke" => "false",
          "Content-Type" => "application/json;charset=UTF-8",
                  "Date" => "Sun, 28 Dec 2014 07:45:54 GMT",
        "Content-Length" => "1268",
            "Connection" => "Close"
}
response.body #=> {
       "code" => "S020010",
    "message" => {
        "textForDisplay" => "インターネットで調べたところ、一位は、まつもとゆきひろです。",
         "textForSpeech" => "インターネットで調べたところ、一位は、マツモトユキヒロです。"
    },
    "answers" => [
        [0] {
                  "rank" => "1",
            "answerText" => "まつもとゆきひろ",
              "linkText" => "田中ばびえ",
               "linkUrl" => "http://d.hatena.ne.jp/keywordmobile/%93c%92%86%82%CE%82%D1%82%A6?kid=177550"
        },
        [1] {
                  "rank" => "2",
            "answerText" => "まつもと",
              "linkText" => "ネット時代の最前線走る3氏が“ビジネスイノベーション\"を語る 角川アスキー総研第1回シンポ開催",
               "linkUrl" => "http://www.zakzak.co.jp/economy/ecn-news/news/20130913/ecn1309130732001-n1.htm"
        },
        [2] {
                  "rank" => "3",
            "answerText" => "DHH",
              "linkText" => "田中ばびえ",
               "linkUrl" => "http://d.hatena.ne.jp/keywordmobile/%93c%92%86%82%CE%82%D1%82%A6?kid=177550"
        },
        [3] {
                  "rank" => "4",
            "answerText" => "高橋征義",
              "linkText" => "ついにRubyの勉強をはじめます - duck75のはてなブログ",
               "linkUrl" => "http://duck75.hatenablog.com/entry/2012/11/26/134640"
        },
        [4] {
                  "rank" => "5",
            "answerText" => "角征典",
              "linkText" => "Amazonアソシエイトやってみようと思いまして - chikuchikugonzalezの雑記帳",
               "linkUrl" => "http://chiku2gonzalez.hatenablog.com/entry/2012/10/19/000248"
        }
    ]
}
```