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/nan/tools/package.json

@@ -0,0 +1,19 @@
+{
+  "name": "1to2",
+  "version": "1.0.0",
+  "description": "NAN 1 -> 2 Migration Script",
+  "main": "1to2.js",
+  "repository": {
+    "type": "git",
+    "url": "git://github.com/nodejs/nan.git"
+  },
+  "contributors": [
+    "Benjamin Byholm <bbyholm@abo.fi> (https://github.com/kkoopa/)",
+    "Mathias Küsel (https://github.com/mathiask88/)"
+  ],
+  "dependencies": {
+    "glob": "~5.0.10",
+    "commander": "~2.8.1"
+  },
+  "license": "MIT"
+}