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/detect-newline/index.js

@@ -0,0 +1,24 @@
+'use strict';
+module.exports = function (str) {
+	if (typeof str !== 'string') {
+		throw new TypeError('Expected a string');
+	}
+
+	var newlines = (str.match(/(?:\r?\n)/g) || []);
+
+	if (newlines.length === 0) {
+		return null;
+	}
+
+	var crlf = newlines.filter(function (el) {
+		return el === '\r\n';
+	}).length;
+
+	var lf = newlines.length - crlf;
+
+	return crlf > lf ? '\r\n' : '\n';
+};
+
+module.exports.graceful = function (str) {
+	return module.exports(str) || '\n';
+};