Fix markdown renderer messes with embedded HTML and support multilingual(unicode)

I fork [showdown_typography](https://github.com/caerphoto/showdown_typography) project.

And solved [#2312](https://github.com/TryGhost/Ghost/issues/2312) issue - Bug: Markdown renderer messes with embedded HTML

In addition, Support non-alphabetic languages.

You can see a live demo [here](http://yangpro.github.io/showdown_typography/).