Slideshow support

this PR uses reveal.js to generate slideshows for each meetup. 

The new meetup.com description formatting is as follows:
```
Presenter1 title
Presenter1 Paragraph1
Presenter1 ParagraphN
-----
Presenter2 title
Presenter2 Paragraph1
Presenter2 ParagraphN
```
note the **5** dashes. This is so we can have arbitrary amounts of description paragraphs.

This is a pretty big dependency, ~100Kb. well, it is compared to 0Kb.

CC @dgreisen, also would you mind updating the debug fixtures, I do not know how to.

**TODO:**

- [ ] only allow this for presentation meetups
- [ ] clean up code
- [ ] find a theme that works better (if that is needed)
- [ ] implement new description formatting for meetup.com