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/source-map-url/.jshintrc

@@ -0,0 +1,43 @@
+{
+  "bitwise": true,
+  "camelcase": true,
+  "curly": false,
+  "eqeqeq": true,
+  "es3": true,
+  "forin": true,
+  "immed": false,
+  "indent": false,
+  "latedef": "nofunc",
+  "newcap": false,
+  "noarg": true,
+  "noempty": true,
+  "nonew": false,
+  "plusplus": false,
+  "quotmark": false,
+  "undef": true,
+  "unused": "vars",
+  "strict": false,
+  "trailing": true,
+  "maxparams": 5,
+  "maxdepth": false,
+  "maxstatements": false,
+  "maxcomplexity": false,
+  "maxlen": 100,
+
+  "asi": true,
+  "expr": true,
+  "globalstrict": true,
+  "smarttabs": true,
+  "sub": true,
+
+  "node": true,
+  "globals": {
+    "describe": false,
+    "it": false,
+    "before": false,
+    "beforeEach": false,
+    "after": false,
+    "afterEach": false,
+    "define": false
+  }
+}