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/strip-eof/index.js

@@ -0,0 +1,15 @@
+'use strict';
+module.exports = function (x) {
+	var lf = typeof x === 'string' ? '\n' : '\n'.charCodeAt();
+	var cr = typeof x === 'string' ? '\r' : '\r'.charCodeAt();
+
+	if (x[x.length - 1] === lf) {
+		x = x.slice(0, x.length - 1);
+	}
+
+	if (x[x.length - 1] === cr) {
+		x = x.slice(0, x.length - 1);
+	}
+
+	return x;
+};