feat. Adding options for %pretrans %posttrans scriptlets

[juliusl]

• During package upgrade, this gives the new package a hook after the old package is uninstalled.

Closes #199

📜 Checklist

• [x] Commits are cleanly separated and have useful messages
• [x] A changelog entry or entries has been added to CHANGELOG.md
• [ ] Documentation is thorough
• [ ] Test coverage is excellent and passes
• [ ] Works when tests are run --all-features enabled

[dralley]

Also needs a changelog entry

[juliusl]

@dralley Addressed all comments and added the flags/prog tag code.

[dralley]

Will finish looking at this tomorrow or Friday

[juliusl]

@dralley No worries, thanks for the review!