Added a new tool: “Remarkise”

*Remarkise* — render your markdown as remark slides, in real time.

Demo: visit [`https://tripu.github.io/remark/remarkise`](https://tripu.github.io/remark/remarkise) and enter the URL of a remark file, eg [`https://github.com/w3c/specberus/blob/master/doc/Presentation.md`](https://github.com/w3c/specberus/blob/master/doc/Presentation.md).