Implement log summary line

Here's some work in progress on #541

Some sample lines:
```json
{
"name":"fxa-auth-server",
"hostname":"moz.local",
"pid":49437,
"level":30,
"op":"request.summary",
"code":200,
"errno":0,
"rid":"1392245543338-49437-23272",
"path":"/v1/account/create",
"remoteAddressChain":["127.0.0.1"],
"t":29,
"email":"935c1cc8f95d79fb287f@restmail.net",
"msg":"",
"time":"2014-02-12T22:52:23.367Z",
"v":0
}
```

```json
{
"name":"fxa-auth-server",
"hostname":"moz.local",
"pid":49459,
"level":30,
"op":"request.summary",
"code":400,
"errno":120,
"rid":"1392245909550-49459-6383",
"path":"/v1/account/login",
"remoteAddressChain":["127.0.0.1"],
"t":2,
"keys":"true",
"email":"8D0E9D02854929B67370@RESTMAIL.NET",
"msg":"",
"time":"2014-02-12T22:58:29.552Z",
"v":0
}
```

I'm currently documenting the mapping from the previous `log.security` lines to `request.summary`