Update KaTeX wrapper to support operation under Node.js

Now we can generate static HTML containing mathematical typesetting

plugins/tiddlywiki/katex/files/tiddlywiki.files

@@ -78,7 +78,9 @@
 				"type": "application/javascript",
 				"title": "$:/plugins/tiddlywiki/katex/katex.min.js",
 				"module-type": "library"
-			}
+			},
+			"prefix": "(function(document) {\n",
+			"suffix": "\n})($tw.node ? $tw.fakeDocument : window.document)\n"
 		}
 	]
 }

plugins/tiddlywiki/katex/wrapper.js

@@ -37,7 +37,11 @@ KaTeXWidget.prototype.render = function(parent,nextSibling) {
 	// Render it into a span
 	var span = this.document.createElement("span");
 	try {
-		katex.render(text,span);
+		if($tw.browser) {
+			katex.render(text,span);
+		} else {
+			span.innerHTML = katex.renderToString(text);
+		}
 	} catch(ex) {
 		span.className = "tc-error";
 		span.textContent = ex;