Feature/http dump cache

[jsvisa]

Add a config of HTTPAddress for the debugging purpose.

HTTPAddress: Specifying an HTTP port for debugging, currently used to dump DNS cache, and the request url is /cache, available query argument is nobody(boolean)

• true(default): only get the cache size;

  $ curl 127.0.0.1:5555/cache | jq
  {
  "length": 1,
  "capacity": 100,
  "body": {}
  }

• false: get cache size along with cache detail.

  $ curl 127.0.0.1:5555/cache?nobody=false | jq
  {
  "length": 1,
  "capacity": 100,
  "body": {
    "www.baidu.com. 1": [
      {
        "name": "www.baidu.com.",
        "ttl": 1140,
        "type": "CNAME",
        "rdata": "www.a.shifen.com."
      },
      {
        "name": "www.a.shifen.com.",
        "ttl": 300,
        "type": "CNAME",
        "rdata": "www.wshifen.com."
      },
      {
        "name": "www.wshifen.com.",
        "ttl": 300,
        "type": "A",
        "rdata": "104.193.88.123"
      },
      {
        "name": "www.wshifen.com.",
        "ttl": 300,
        "type": "A",
        "rdata": "104.193.88.77"
      }
    ]
  }
  }

[shawn1m]

Merged, thanks!