A first pass at fixing #2973 - comments are welcome. If everybody is
happy, the next step is to deprecate the existing
rendertiddler(s)/savetiddler(s) commands and replace them in all
examples and tiddlywiki.info files with the new equivalents.
This change is likely to break most existing scripts that call
TiddlyWiki.
TL;DR - output paths are now relative to the editions/output folder,
rather than to the current folder
See [[Notes for upgrading to 5.0.11-beta]] for details.