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/ajv/lib/dotjs/comment.js

@@ -0,0 +1,14 @@
+'use strict';
+module.exports = function generate_comment(it, $keyword, $ruleType) {
+  var out = ' ';
+  var $schema = it.schema[$keyword];
+  var $errSchemaPath = it.errSchemaPath + '/' + $keyword;
+  var $breakOnError = !it.opts.allErrors;
+  var $comment = it.util.toQuotedString($schema);
+  if (it.opts.$comment === true) {
+    out += ' console.log(' + ($comment) + ');';
+  } else if (typeof it.opts.$comment == 'function') {
+    out += ' self._opts.$comment(' + ($comment) + ', ' + (it.util.toQuotedString($errSchemaPath)) + ', validate.root.schema);';
+  }
+  return out;
+}