Major refactoring of filesystemadaptor

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.

core/modules/utils/utils.js

@@ -697,7 +697,6 @@ exports.tagToCssSelector = function(tagName) {
 	});
 };
 
-
 /*
 IE does not have sign function
 */
@@ -725,4 +724,82 @@ exports.strEndsWith = function(str,ending,position) {
 	}
 };
 
+/*
+Transliterate string from eg. Cyrillic Russian to Latin
+*/
+var transliterationPairs = {
+	"Ё":"YO",
+	"Й":"I",
+	"Ц":"TS",
+	"У":"U",
+	"К":"K",
+	"Е":"E",
+	"Н":"N",
+	"Г":"G",
+	"Ш":"SH",
+	"Щ":"SCH",
+	"З":"Z",
+	"Х":"H",
+	"Ъ":"'",
+	"ё":"yo",
+	"й":"i",
+	"ц":"ts",
+	"у":"u",
+	"к":"k",
+	"е":"e",
+	"н":"n",
+	"г":"g",
+	"ш":"sh",
+	"щ":"sch",
+	"з":"z",
+	"х":"h",
+	"ъ":"'",
+	"Ф":"F",
+	"Ы":"I",
+	"В":"V",
+	"А":"a",
+	"П":"P",
+	"Р":"R",
+	"О":"O",
+	"Л":"L",
+	"Д":"D",
+	"Ж":"ZH",
+	"Э":"E",
+	"ф":"f",
+	"ы":"i",
+	"в":"v",
+	"а":"a",
+	"п":"p",
+	"р":"r",
+	"о":"o",
+	"л":"l",
+	"д":"d",
+	"ж":"zh",
+	"э":"e",
+	"Я":"Ya",
+	"Ч":"CH",
+	"С":"S",
+	"М":"M",
+	"И":"I",
+	"Т":"T",
+	"Ь":"'",
+	"Б":"B",
+	"Ю":"YU",
+	"я":"ya",
+	"ч":"ch",
+	"с":"s",
+	"м":"m",
+	"и":"i",
+	"т":"t",
+	"ь":"'",
+	"б":"b",
+	"ю":"yu"
+};
+
+exports.transliterate = function(str) {
+	return str.split("").map(function(char) {
+		return transliterationPairs[char] || char;
+	}).join("");
+};
+
 })();