Feature Request: add attributes

@scottdeluzio
Hi Scott,
I have long wanted to be able to insert a complete shortcode to the editor, so I was glad to see your plugin.
However, it stops short of being totally useful.
I have written a proof of concept for a way to get the attributes of a shortcode, and I wondered if you could test it out and make it robust to add to your plugin.

I imported your plugin to GitHub, but it stopped short of full import, and left me with version 1.0.3 or something like that. I created a branch for my concept here: https://github.com/joyously/shortcode-lister/tree/feature-standalone
(I was originally trying to do this for inclusion in ClassicPress and had the wrong idea, so the name was changed from lister to list.)

I think it needs testing on different PHP versions, as I’m not sure that the output remains the same. It needs the booleans filtered to 0 or 1; you can see this in either the [embed] or [video]. I intended that there be JS for the editor to better handle the editing of the shortcode, but didn’t get to that part.
The reason I did this the way I did is it made sense to deal with a keyed array in PHP rather than JS, and the var_export function made it so easy regarding types and quotes, etc.

I hope you see the value of this and can incorporate it into your plugin.
Joy