Review and add CVE fixes dataset

[pombredanne]

See https://zenodo.org/records/7029359 and https://github.com/secureIT-project/CVEfix

[armijnhemel]

The latter URL should be: https://github.com/secureIT-project/CVEfixes

[ziadhany]

This is done:

• Add support for parsing Git commit messages #1992

For the CVEfixes dataset, we collect fix commits in a similar way to what is implemented here:

https://github.com/secureIT-project/CVEfixes/blob/main/Code/collect_commits.py#L76