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/is-callable/.eslintrc

@@ -0,0 +1,11 @@
+{
+	"root": true,
+
+	"extends": "@ljharb",
+
+	"rules": {
+		"id-length": 0,
+		"max-statements": [2, 12],
+		"max-statements-per-line": [2, { "max": 2 }]
+	}
+}