Code blocks in requirements break parsing

[jakobbraun]

Adding a code block like:

```md
## Test

test 123
```

... to the requirements file breaks the parsing. OFT seems to detect it as a new requirement.

Expected Behaviour:

• OFT ignored the headline in the code block (important)
• OFT prints the contents of the code block formated as code in the HTML output (nice to have)

[redcatbear]

I think I can solve this by adding a new state in the markdown parser that ignores literal sections (starting and ending with tripple-backticks).

[koppor]

Similar behavior when requirement ids are in the blocks

Example

...

```markdown
### Chatting with AI
`req~ai.chat.new-message-based-on-previous~1`
```

Then, at the implementation, a comment is added this implementation is covered:

```java
} else if (keyEvent.getCode() == KeyCode.UP) {
 // [impl->req~ai.chat.new-message-based-on-previous~1]
```

[redcatbear]

I checked the GMF spec from which the fenced code blocks come. That spec allows quite a range of variants to start a code block. I tried to capture the reasonable part in the parser in #433 without making it a lot more complex.