Replace chapter 4 with gists, blocks and blockbuilder

[Fil]

Learning git seems to be too much load for this lesson.

It's probably an easier path to learn to create gists, and you'll have covered half the way to properly using Github.

With gists we get access to the d3 ecosystem of bl.ocks.org and blockbuilder.

Also it takes some pressure off “publishing”, just because it looks more like “playground”. We can even start with anonymous gists!

[Fil]

Note that one sad consequence of this choice is that we would lose the possibility to use alert() in the examples, at least with blockbuilder.

[IsaKiko]

Hm - interesting idea!

I'm personally a big fan of making everyone putting their things online. I also think it's fantastic seeing that you are able to create a webpage and put it online within a day!
Having said that, the github lesson needs some work. It's easier now to add files to a repo using only the online interface. So there's no need to download anything anymore.

I haven't really used gists. How would that work? And how does the integration into bl.ocks work?

Loosing alerts is a little bit sad.. it seems people really enjoy them on their first toy pages (although I encourage them to quickly move on from alerts after ;))

[Fil]

blocks are just a way to display gists directly in the browser ; it was
made by Mike Bostock to showcase the D3 examples.

blockbuilder is a website that displays blocks/gists, but also enables to
toy with their code directly in the browser, in realtime, saving and
forking as you go (and only if you need). It's the fastest way to interact
with d3 code.

Limitations are:

• no modal dialogs on blockbuilder (but solutions are coming, see
  making something for alert() enjalot/blockbuilder#144 )
• no sub-directories in gists (when your project becomes a bit more complex
  you have to move it to a "real" github repo)

As both blocks and blockbuilder use github gists as their file backend,
everything that exists in gist space also exists in blocks and blockbuilder
space, and vice versa. There is even a handy bookmarklet to "jump" from a
block to the blockbuilder page. (And the URL structure is the same)

-- Fil