GAP upstream asked me to change the GAP packages from a single unified installation under /usr/lib/gap to a split installation, with arch-specific packages in %{_libdir}/gap and noarch packages in %{_datadir}/gap. I have made that change for F38+. This necessitates some changes to the GAP packaging guidelines. The changes are as follows:

• Update the guidelines to reflect the new split installation trees.
• Remove bad advice about having multiple ExclusiveArch tags in a single spec file.

This PR contains the changes, along with some minor clarifications and presentation improvements: https://pagure.io/packaging-committee/pull-request/1250