The intent of existing .gitignore was to ignore some directories
at repository root.
Instead, it was ignoring any file or directory by given names,
anywhere in the tree.
Improve rules to only match the intended cases.
Also, add new item for builder.sh's temporary file.
Restart the repository by
1. Starting to use Antora
2. Moving over some packaging related pages over from the wiki
3. Updating the pages where there are obvious problems