New macros for API template

[petrdvorak]

In case we render data in API template, we should be able to interpret the follwing macros...

API root

<!-- begin API -->
    xxx
    <!-- begin API-PATH POST /some/path -->
        yyy
    <!-- end API-PATH POST -->
    <!-- begin API-REQUEST -->
        zzz
    <!-- end API-REQUEST -->
    <!-- begin API-RESPONSE -->
        www
        <!-- begin API-RESPONSE-TAB 200 -->
            hhh
        <!-- end API-RESPONSE-TAB -->
    <!-- end API-RESPONSE -->
<!-- end API -->

... translate to:

{% api %}
xxx
{% apipath POST /some/path %}
yyy
{% endapipath %}
{% apirequest %}
zzz
{% endapirequest %}
{% apiresponse %}
www
{% apiresponsetab %}
hhh
{% endapiresponsetab %}
{% endapiresponse %}
{% endapi %}

[petrdvorak]

Let's use a slightly more complex definition of endpoint:

<!-- begin API-PATH POST /some/path "Some path" -->

Such as:

<!-- begin API-PATH PUT /article "Edit article" -->

In other words, we should also define the "name" of the endpoint to be included in the menu...

[petrdvorak]

So... one more improvement - I promise it is the last one. :) I introduced a new {% apidescription %} tag for an API description. Here is the example of an expected markup:

<!-- begin API -->
<!-- begin API-PATH POST /note/edit "Edit Note" -->
### POST /note/edit
<!-- end API-PATH POST -->
<!-- begin API-DESCRIPTION -->
Edit an exisiting note.
<!-- end API-DESCRIPTION -->
<!-- begin API-REQUEST -->

{ "id": "12", "text": "Updated text" }

<!-- end API-REQUEST -->
<!-- begin API-RESPONSE -->
<!-- begin API-RESPONSE-TAB 200 -->

{ "status": "OK" }

<!-- end API-RESPONSE-TAB -->
<!-- begin API-RESPONSE-TAB 401 -->

{ "status": "ERROR", "message": "401 Unauthorized" }

<!-- end API-RESPONSE-TAB -->
<!-- end API-RESPONSE -->
<!-- end API -->

[hvge]

Depends on #48

[hvge]

OK, hope this is the final format:

<!-- begin API POST /note/edit -->

### Edit note

Edit an exisiting note.

#### Request
```
{
    "id": "12",
    "text": "Updated text"
}
```
#### Response 200
```
{
    "status": "OK"
}
```
#### Response 400
```
{
    "status": "ERROR",
    "message": "401 Unauthorized"
}
```
<!-- end -->

Where

• L3 heading defines title of API block
• Everything after L3 heading, up to next heading, defines description section
• L4 heading with "Request" title, defines request section
• L4 heading with "Response XXX" title, defines response & response tab section

[petrdvorak]

@hvge It looks good in general but does not handle situations where no request description is present. Sometimes, the request is fully defined by the API definition (method + URI). This markup does not render correctly:

<!-- begin api GET /push/service/status -->
### Service Status

Send a system status response, with basic information about the running application.

<!-- begin remove -->
<table>
    <tr>
        <td>Method</td>
        <td><code>GET</code></td>
    </tr>
    <tr>
        <td>Resource URI</td>
        <td>/push/service/status</td>
    </tr>
</table>
<!-- end -->

#### Response 200

```json
{
  "status": "OK",
  "responseObject": {
    "applicationName": "powerauth-push",
    "applicationDisplayName": "PowerAuth Push Server",
    "applicationEnvironment": "",
    "version": "0.21.0",
    "buildTime": "2019-01-22T14:59:14.954+0000",
    "timestamp": "2019-01-22T15:00:28.399+0000"
  }
}

• applicationName - Application name.
• applicationDisplayName - Application display name.
• applicationEnvironment - Application environment.
• version - Version of Push server.
• buildTime - Timestamp when the powerauth-push-server.war file was built.
• timestamp - Current time on application.

[petrdvorak]

Also, documentation with nested headers does not seem to work well:

<!-- begin api PUT /push/campaign/${id}/user/add -->
### Add Users To Campaign

Associate users to a specific campaign. Users are identified in request body as an array of strings.

#### Request

<!-- begin remove -->
<table>
    <tr>
        <td>Method</td>
        <td><code>POST / PUT</code></td>
    </tr>
    <tr>
        <td>Resource URI</td>
        <td>/push/campaign/${ID}/user/add</td>
    </tr>
</table>
<!-- end -->

##### Query Parameters

<table>
    <tr>
        <td>id</td>
        <td>Campaign identifier</td>
    </tr>
</table>

##### Request Body

```json
{
  "requestObject": [
    "1234567890",
    "1234567891",
    "1234567893"
  ]
}

• list of users

Response 200

{
  "status": "OK"
}