Fixes

I've imported 2 files from the native ST markdown plugin and improved one of it. This PR makes it possible to see such a list when pressed <kbd>Ctrl</kbd> <kbd>R</kbd> in a markdown file:

![screen](https://f.cloud.github.com/assets/844008/1384083/7a0b8a50-3b48-11e3-84db-86c983324f31.png)

Edit: Fixes #47.