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/object.getownpropertydescriptors/test/.eslintrc

@@ -0,0 +1,8 @@
+{
+	"rules": {
+		"max-nested-callbacks": [2, 3],
+		"max-statements": [2, 15],
+		"max-statements-per-line": [2, { "max": 2 }],
+		"no-invalid-this": [1]
+	}
+}