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/minimist/test/long.js

@@ -0,0 +1,31 @@
+var test = require('tape');
+var parse = require('../');
+
+test('long opts', function (t) {
+    t.deepEqual(
+        parse([ '--bool' ]),
+        { bool : true, _ : [] },
+        'long boolean'
+    );
+    t.deepEqual(
+        parse([ '--pow', 'xixxle' ]),
+        { pow : 'xixxle', _ : [] },
+        'long capture sp'
+    );
+    t.deepEqual(
+        parse([ '--pow=xixxle' ]),
+        { pow : 'xixxle', _ : [] },
+        'long capture eq'
+    );
+    t.deepEqual(
+        parse([ '--host', 'localhost', '--port', '555' ]),
+        { host : 'localhost', port : 555, _ : [] },
+        'long captures sp'
+    );
+    t.deepEqual(
+        parse([ '--host=localhost', '--port=555' ]),
+        { host : 'localhost', port : 555, _ : [] },
+        'long captures eq'
+    );
+    t.end();
+});