resolves #57 consolidate cache folders under .antora-cache
- move .git-cache to .antora-cache/content
- move .ui-cache to .antora-cache/ui
- add constants file for ui-loader
- add explicit dependency on fs-extra
- use fs.ensureDirSync instead of async version w/ await
- cleanup imports
- generate a more friendly folder name for cloned repos
Edited by Dan Allen