Drop unexpected columns when writing PDB dataframes #124

[a-r-j]

Code of Conduct

Description

Drop non standard columsn from ATOM and HETATM dataframes when exporting to a PDB file.

cc @amorehead

Related issues or pull requests

#124

Pull Request Checklist

• [ ] Added a note about the modification or contribution to the ./docs/sources/CHANGELOG.md file (if applicable)
• [ ] Added appropriate unit test functions in the ./biopandas/*/tests directories (if applicable)
• [ ] Modify documentation in the corresponding Jupyter Notebook under biopandas/docs/sources/ (if applicable)
• [ ] Ran PYTHONPATH='.' pytest ./biopandas -sv and make sure that all unit tests pass (for small modifications, it might be sufficient to only run the specific test file, e.g., PYTHONPATH='.' pytest ./biopandas/classifier/tests/test_stacking_cv_classifier.py -sv)
• [ ] Checked for style issues by running flake8 ./biopandas