Added checks to make sure the specified track exists

Added precondition checks to validate input files and paths to return more informative error messages as per #2

node_modules/xml-name-validator/lib/xml-name-validator.js

@@ -0,0 +1,17 @@
+"use strict";
+const parser = require("./generated-parser.js");
+
+exports.name = function (potentialName) {
+    return mapResult(parser.startWith("Name").exec(potentialName));
+};
+
+exports.qname = function (potentialQname) {
+    return mapResult(parser.startWith("QName").exec(potentialQname));
+};
+
+function mapResult(result) {
+    return {
+        success: result.success,
+        error: result.error && parser.getTrace(result.error.message)
+    };
+}