Add markdown format support (#25)

Co-authored-by: Dawid Dziurla <dawidd0811@gmail.com>

node_modules/yargs/lib/yerror.js

@@ -0,0 +1,11 @@
+'use strict'
+function YError (msg) {
+  this.name = 'YError'
+  this.message = msg || 'yargs error'
+  Error.captureStackTrace(this, YError)
+}
+
+YError.prototype = Object.create(Error.prototype)
+YError.prototype.constructor = YError
+
+module.exports = YError