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/handlebars/lib/handlebars.runtime.js

@@ -0,0 +1,37 @@
+import * as base from './handlebars/base';
+
+// Each of these augment the Handlebars object. No need to setup here.
+// (This is done to easily share code between commonjs and browse envs)
+import SafeString from './handlebars/safe-string';
+import Exception from './handlebars/exception';
+import * as Utils from './handlebars/utils';
+import * as runtime from './handlebars/runtime';
+
+import noConflict from './handlebars/no-conflict';
+
+// For compatibility and usage outside of module systems, make the Handlebars object a namespace
+function create() {
+  let hb = new base.HandlebarsEnvironment();
+
+  Utils.extend(hb, base);
+  hb.SafeString = SafeString;
+  hb.Exception = Exception;
+  hb.Utils = Utils;
+  hb.escapeExpression = Utils.escapeExpression;
+
+  hb.VM = runtime;
+  hb.template = function(spec) {
+    return runtime.template(spec, hb);
+  };
+
+  return hb;
+}
+
+let inst = create();
+inst.create = create;
+
+noConflict(inst);
+
+inst['default'] = inst;
+
+export default inst;