Added health check results to embedded tasks

- Fixes #583 
- Includes docs changes

Works now for the apps collection:

```http
GET /v2/apps?embed=apps.tasks HTTP/1.1
Accept: */*
Accept-Encoding: gzip, deflate
Host: mesos.vm:8080
User-Agent: HTTPie/0.8.0
```

```http
HTTP/1.1 200 OK
Content-Type: application/json
Server: Jetty(8.y.z-SNAPSHOT)
Transfer-Encoding: chunked

{
    "apps": [
        {
            "args": null, 
            "backoffFactor": 1.15, 
            "backoffSeconds": 1, 
            "cmd": "python toggle.py $PORT0", 
            "constraints": [], 
            "container": null, 
            "cpus": 0.2, 
            "dependencies": [], 
            "deployments": [], 
            "disk": 0.0, 
            "env": {}, 
            "executor": "", 
            "healthChecks": [
                {
                    "command": null, 
                    "gracePeriodSeconds": 5, 
                    "intervalSeconds": 10, 
                    "maxConsecutiveFailures": 3, 
                    "path": "/health", 
                    "portIndex": 0, 
                    "protocol": "HTTP", 
                    "timeoutSeconds": 10
                }
            ], 
            "id": "/toggle", 
            "instances": 2, 
            "mem": 32.0, 
            "ports": [
                10000
            ], 
            "requirePorts": false, 
            "storeUrls": [], 
            "tasks": [
                {
                    "appId": "/toggle", 
                    "healthCheckResults": [
                        {
                            "alive": true, 
                            "consecutiveFailures": 0, 
                            "firstSuccess": "2014-09-13T00:20:28.101Z", 
                            "lastFailure": null, 
                            "lastSuccess": "2014-09-13T00:21:37.114Z", 
                            "taskId": "toggle.802df2ae-3ad4-11e4-a400-56847afe9799"
                        }
                    ], 
                    "host": "10.141.141.10", 
                    "id": "toggle.802df2ae-3ad4-11e4-a400-56847afe9799", 
                    "ports": [
                        31045
                    ], 
                    "stagedAt": "2014-09-12T23:28:28.594Z", 
                    "startedAt": "2014-09-13T00:21:16.958Z", 
                    "version": "2014-09-12T23:28:21.737Z"
                }, 
                {
                    "appId": "/toggle", 
                    "healthCheckResults": [
                        {
                            "alive": true, 
                            "consecutiveFailures": 0, 
                            "firstSuccess": "2014-09-13T00:20:28.101Z", 
                            "lastFailure": null, 
                            "lastSuccess": "2014-09-13T00:21:37.112Z", 
                            "taskId": "toggle.7c99814d-3ad4-11e4-a400-56847afe9799"
                        }
                    ], 
                    "host": "10.141.141.10", 
                    "id": "toggle.7c99814d-3ad4-11e4-a400-56847afe9799", 
                    "ports": [
                        31234
                    ], 
                    "stagedAt": "2014-09-12T23:28:22.587Z", 
                    "startedAt": "2014-09-13T00:21:16.966Z", 
                    "version": "2014-09-12T23:28:21.737Z"
                }
            ], 
            "tasksRunning": 2, 
            "tasksStaged": 0, 
            "upgradeStrategy": {
                "minimumHealthCapacity": 1.0
            }, 
            "uris": [
                "http://downloads.mesosphere.io/misc/toggle.tgz"
            ], 
            "user": null, 
            "version": "2014-09-12T23:28:21.737Z"
        }
    ]
}
```

and for the app resource:

```http
GET /v2/apps/toggle?embed=apps.tasks HTTP/1.1
Accept: */*
Accept-Encoding: gzip, deflate
Host: mesos.vm:8080
User-Agent: HTTPie/0.8.0
```

```http
HTTP/1.1 200 OK
Content-Type: application/json
Server: Jetty(8.y.z-SNAPSHOT)
Transfer-Encoding: chunked

{
    "app": {
        "args": null, 
        "backoffFactor": 1.15, 
        "backoffSeconds": 1, 
        "cmd": "python toggle.py $PORT0", 
        "constraints": [], 
        "container": null, 
        "cpus": 0.2, 
        "dependencies": [], 
        "deployments": [], 
        "disk": 0.0, 
        "env": {}, 
        "executor": "", 
        "healthChecks": [
            {
                "command": null, 
                "gracePeriodSeconds": 5, 
                "intervalSeconds": 10, 
                "maxConsecutiveFailures": 3, 
                "path": "/health", 
                "portIndex": 0, 
                "protocol": "HTTP", 
                "timeoutSeconds": 10
            }
        ], 
        "id": "/toggle", 
        "instances": 2, 
        "mem": 32.0, 
        "ports": [
            10000
        ], 
        "requirePorts": false, 
        "storeUrls": [], 
        "tasks": [
            {
                "appId": "/toggle", 
                "healthCheckResults": [
                    {
                        "alive": true, 
                        "consecutiveFailures": 0, 
                        "firstSuccess": "2014-09-13T00:20:28.101Z", 
                        "lastFailure": null, 
                        "lastSuccess": "2014-09-13T00:25:07.506Z", 
                        "taskId": "toggle.802df2ae-3ad4-11e4-a400-56847afe9799"
                    }
                ], 
                "host": "10.141.141.10", 
                "id": "toggle.802df2ae-3ad4-11e4-a400-56847afe9799", 
                "ports": [
                    31045
                ], 
                "stagedAt": "2014-09-12T23:28:28.594Z", 
                "startedAt": "2014-09-13T00:24:46.959Z", 
                "version": "2014-09-12T23:28:21.737Z"
            }, 
            {
                "appId": "/toggle", 
                "healthCheckResults": [
                    {
                        "alive": true, 
                        "consecutiveFailures": 0, 
                        "firstSuccess": "2014-09-13T00:20:28.101Z", 
                        "lastFailure": null, 
                        "lastSuccess": "2014-09-13T00:25:07.508Z", 
                        "taskId": "toggle.7c99814d-3ad4-11e4-a400-56847afe9799"
                    }
                ], 
                "host": "10.141.141.10", 
                "id": "toggle.7c99814d-3ad4-11e4-a400-56847afe9799", 
                "ports": [
                    31234
                ], 
                "stagedAt": "2014-09-12T23:28:22.587Z", 
                "startedAt": "2014-09-13T00:24:46.965Z", 
                "version": "2014-09-12T23:28:21.737Z"
            }
        ], 
        "tasksRunning": 2, 
        "tasksStaged": 0, 
        "upgradeStrategy": {
            "minimumHealthCapacity": 1.0
        }, 
        "uris": [
            "http://downloads.mesosphere.io/misc/toggle.tgz"
        ], 
        "user": null, 
        "version": "2014-09-12T23:28:21.737Z"
    }
}
```

@ssorallen