Pagetools

Bugfix
- fixed using RGB instead of BGR – as required by cv2 – for the background color in `Line2Page` thanks to jahtz

Bugfix
- Explicitly specifies output encoding in `get-codec` to avoid Unicode errors under Windows

Features
- [migrated from setup.py to pyproject.toml](https://github.com/uniwue-zpd/PAGETools/commit/08c6c2723b760bdc15bd5473a8b7bceab6c1f9f3)
Bugfix
- [fix (setup): fix error in entry point declaration](https://github.com/uniwue-zpd/PAGETools/commit/1a9453dd8630b3ddc65711ede8d147fec8a8aa89) thanks to martholomew
- various other small fixes

Features
* added line2page as new tool
* minor updates to the README and docstrings
* added basic test environment

Bugfixes
* fixes punctuation ruleset to correctly normalize multiple whitespaces