Auto detect slide title for markdown slides

[thawk]

We can use the first non-blank line for markdown title. For a regular presentation, the first line may be suitable for title.
I think it's better than the step-X, and can easy navigation.

[henrikingo]

Can you give an example of what you mean?

The intended usage is:

# Slide title

Some text

## Sub-title

* bullet point

In other words, normal Markdown syntax. Are you proposing to add functionality where the first line becomes a title, even if the author didnt necessarily want that?

[thawk]

For example, with the example examples/markdown/index.html, in the bottom-right goto dropbox, it shows markdown/step-2/step-3/step-4.... It's hard to select a correct slide to goto.

To get a meaningful title, we can use the first line of each slide. I think the first line of a slide should be the most important sentence at most time. With this, the titles of the above example will be markdown/Markdown.js/Styles/A blockquote & image/Code/Slide separator/Title slide... I think it's much easier to goto the right slide.

---

For the following example, there will be 3 slides, titled Slide title/Sub-title/Another point.

# Slide title

Some text

-----

## Sub-title

* bullet point

## Sub-title2

* some thing

-----

Another point

[henrikingo]

Ah, thanks for clarifying. This makes sense.

[thawk]

Closed by #821