httpcaddyfile: Support single-line matchers

[francislavoie]

I think this is a big win for readability. Almost identical implementation to #3228.

Caddyfile:

:80 {
    @matcher {
        method GET
    }
    respond @matcher "get"

    @matcher2 method POST
    respond @matcher2 "post"

    @matcher3 not method PUT
    respond @matcher3 "not put"
}

JSON:

{
  "apps": {
    "http": {
      "servers": {
        "srv0": {
          "listen": [
            ":80"
          ],
          "routes": [
            {
              "match": [
                {
                  "method": [
                    "GET"
                  ]
                }
              ],
              "handle": [
                {
                  "body": "get",
                  "handler": "static_response"
                }
              ]
            },
            {
              "match": [
                {
                  "method": [
                    "POST"
                  ]
                }
              ],
              "handle": [
                {
                  "body": "post",
                  "handler": "static_response"
                }
              ]
            },
            {
              "match": [
                {
                  "not": [
                    {
                      "method": [
                        "PUT"
                      ]
                    }
                  ]
                }
              ],
              "handle": [
                {
                  "body": "not put",
                  "handler": "static_response"
                }
              ]
            }
          ]
        }
      }
    }
  }
}

[mholt]

I still can't believe that works.

Let's see how it goes!