CRLF line endings are not parsed correctly.

The CommmonMark spec [requires CR and CRLF](https://spec.commonmark.org/0.29/#line-ending) to be supported as line endings, but this library parses CRLF incorrectly. For example:

```kotlin
MarkdownParser(CommonMarkFlavourDescriptor()).buildMarkdownTreeFromString("a \r\nb")
```

parses as:

```
Markdown:PARAGRAPH
Markdown:TEXT 'a'
Markdown:BR '·␍'
Markdown:EOL '␊'
Markdown:TEXT 'b'
```

and renders as:

```

a

b