Rename gone -> stray

[foriequal0]

gone is coined after git's gone branch. It was the start of the git-trim. However, gone is not gone anymore. It is more subtle to call it gone.
I propose to rename them to stray.

I wanted them to be conceived as not safe to delete. stray is the opposite of merged. It is not merged, not safe to delete, but it exists out there. It needs extra care.