Fixes#3875
* Use .json files (instead of .tid) for any tiddler whose fields contain values that can't be stored as a .tid file
* Save application/json tiddlers as .json files
* Refactor most of the file handling as re-usable utilities
When saving new tiddlers on node.js, allow the user to override the path of the
generated .tid file. This is done by creating a tiddler
$:/config/FileSystemPaths which contains one or more filter expressions, one
per line. These filters are applied in turn to the tiddler to be saved, and
the first output produced is taken as a logical path relative to the wiki's
tiddlers directory. Any occurences of "/" in the logical path are replaced with
the platform's path separator, the extension ".tid" is appended, illegal
characters are replaced by "_" and the path is disambiguated (if necessary) in
order to arrive at the final tiddler file path. If none of the filters matches,
or the configuration tiddler does not exist, fall back to the previous file
naming scheme (i.e. replacing "/" by "_").
This implies we will now, for tiddlers matching the user-specified filters,
create directory trees below the tiddlers directory. In order to avoid
cluttering it with empty directory trees when renaming or removing tiddlers, any
directories that become empty by deleting a tiddler file are removed
(recursively).
Benefits of this configuration option include the ability to organize git
repositories of TiddlyWikis running on node.js, ability to replace characters
that cause trouble with particular operating systems or workflows (e.g. '$' on
unix) and the ability to replicate tiddler "paths" in the filesystem (by
including a filter like "[!has[draft.of]]") without forcing such a (potentially
problematic) change on all users.
There are still some warnings about making functions in a loop, but
I’ll fix those as a separate pull request because the fixes are more
than typographic errors.
