The functions to calculate file checksums and package verification codes have been removed during the refactoring for v0.8. However, I found out that they are indeed being used, [for example by scancode](https://github.com/nexB/scancode-toolkit/blob/a15174f31efaf8816e8c9a65c9f85c4beffc0227/src/formattedcode/output_spdx.py#L406). To allow libraries to upgrade, we should add back this functionality.