The code here had got a bit broken by some PRs that I should have
checked more carefully. I’ve done a major refactoring which will
hopefully make it easier to understand, and fixes a number of problems:
* Problem with eg .md tiddlers not being deleted correctly
* Problem with Windows path separators not being usable within
$:/config/FileSystemPaths on Windows
* Problem with filename clashes not being detected correctly when
saving to a different directory via $:/config/FileSystemPaths
* Enables slashes within tiddler titles to be mapped into folders
* Enables plain text files like .md and .css to be saved with .meta
files instead of as .tid files (see #2558)
* No longer replaces spaces with underscores
As this is such a major update, I’d be grateful if Node.js users could
give it a careful run through — in particular, you’ll need to try
creating new tiddlers of various types and ensure that the expected
files are created.
