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/tsconfig.json

@@ -0,0 +1,20 @@
+{
+    "compilerOptions": {
+        "module": "es2015",
+        "target": "esnext",
+        "noImplicitAny": true,
+        "sourceMap": true,
+        "alwaysStrict": true,
+        "declaration": true,
+        "experimentalDecorators": true,
+        "forceConsistentCasingInFileNames": true,
+        "importHelpers": true,
+        "noImplicitReturns": true,
+        "noImplicitThis": true,
+        "outDir": "dist/esnext",
+        "strictNullChecks": true
+    },
+    "include": [
+        "src/**/*"
+    ]
+}