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/lodash/ceil.js

@@ -0,0 +1,26 @@
+var createRound = require('./_createRound');
+
+/**
+ * Computes `number` rounded up to `precision`.
+ *
+ * @static
+ * @memberOf _
+ * @since 3.10.0
+ * @category Math
+ * @param {number} number The number to round up.
+ * @param {number} [precision=0] The precision to round up to.
+ * @returns {number} Returns the rounded up number.
+ * @example
+ *
+ * _.ceil(4.006);
+ * // => 5
+ *
+ * _.ceil(6.004, 2);
+ * // => 6.01
+ *
+ * _.ceil(6040, -2);
+ * // => 6100
+ */
+var ceil = createRound('ceil');
+
+module.exports = ceil;