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/uri-js/src/index.ts

@@ -0,0 +1,18 @@
+import { SCHEMES } from "./uri";
+
+import http from "./schemes/http";
+SCHEMES[http.scheme] = http;
+
+import https from "./schemes/https";
+SCHEMES[https.scheme] = https;
+
+import mailto from "./schemes/mailto";
+SCHEMES[mailto.scheme] = mailto;
+
+import urn from "./schemes/urn";
+SCHEMES[urn.scheme] = urn;
+
+import uuid from "./schemes/urn-uuid";
+SCHEMES[uuid.scheme] = uuid;
+
+export * from "./uri";