[orchestra2md] Actor and Flow documentation content is added before the Markdown heading

[JThoennes]

    <fixr:actors>
        <fixr:actor name="TradingAdapter">
            <fixr:annotation>
                <fixr:documentation contentType="text/markdown">This actor connects the BLOXX Order Management to the Trading System of the customer.</fixr:documentation>
            </fixr:annotation>
        </fixr:actor>
        <fixr:actor name="TradingSystem">
            <fixr:annotation>
                <fixr:documentation contentType="text/markdown">This is the customers Trading System receiving orders from the Trading Adapter and sending executions back.</fixr:documentation>
            </fixr:annotation>
        </fixr:actor>
    </fixr:actors>

is rendered in Markdown as:

## Actors and Flows

This actor connects the BLOXX Order Management to the Trading System of the customer.

### Actor TradingAdapter

This is the customers Trading System receiving orders from the Trading Adapter and sending executions back.

### Actor TradingSystem

It seems the fixr:documentation contents is added before the related heading.

[JThoennes]

The same applies to the documentation element of a fixr:flow element.

[JThoennes]

@donmendelson Just tested it locally. Now the headings appear twice in the Markdown (content meanwhile change a bit...):

## Actors and Flows

### Actor ClientOrderSender

This actor resembles the BLOXX FIX Trading Adapter in Client Order mode. It connects the BLOXX Order Management to the Trading System of the customer.

### Actor ClientOrderSender

### Actor BlockOrderSender

This actor resembles the BLOXX FIX Trading Adapter in Block Order mode. It connects the BLOXX Order Management to the Trading System of the customer.

### Actor BlockOrderSender

### Actor TradingSystem

Thanks for the prompt commit!

[JThoennes]

@donmendelson I think my second PR solves this issue. But a test is missing.