Nbresult

Added

- Support subdirectory in commit step
- Tests support subdirectory in commit step

Added

- Tests

Removed

- `requirements.txt` as the package should rely as much as possible on the Python Standard Library
- `nbresult_checker` as it has a dependency with an internal package

Added

- Allow specify a `subdir` folder in which store/read pickle file

Added

- Adds `nbresult_checker` script listing pickle files containing complex python data types