`AnnotatedText`: Erroneous processing of texts containing the `\n` literal sequence

The issue can probably best be demonstrated with an example:

```python
from ua_gec import AnnotatedText

text = AnnotatedText(r'\n{=>_}')
print(len(text.get_original_text()))  # output: 1
print(text.get_annotations()[0].start)  # output: 2
```