D1919 Rework README.md and remove broken links.

I reworked github markdown syntax quite a bit. The key phrase mobile shopping cart will gain more search results. Not sure if I got the project trademark correct or not.

The roadmap link was broken. I've linked github contributions for this project, the developer forums, where to ask a feature request, documentation, and new h2 for the OGP feature you have released. There is also the GPL V2 preamble at the bottom.

The very last section you see in source is markdown reference links. They don't show up. To make them, use my example. To use them, only need insert the variable. [example reference link] into content after defined.