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/qs/test/.eslintrc

@@ -0,0 +1,15 @@
+{
+    "rules": {
+		"array-bracket-newline": 0,
+		"array-element-newline": 0,
+		"consistent-return": 2,
+        "max-lines": 0,
+        "max-nested-callbacks": [2, 3],
+        "max-statements": 0,
+		"no-buffer-constructor": 0,
+        "no-extend-native": 0,
+        "no-magic-numbers": 0,
+		"object-curly-newline": 0,
+        "sort-keys": 0
+    }
+}