Pass custom arrow image URL

[epalmans]

Exposes a second optional parameter to the show() method which allows to override the default orange one. Works by removing the original node and events from the DOM first; then regenerates it using _initArrow().

Example usage: <a href="#" onclick="Arrow.show(5000, 'https://i.imgur.com/MZRB3eb.png')">Download</a>

Note:

• not provided: jsdoc
• not provided: tests
• you may want to consider passing a config. object to the show() method