Add Livebook README

[tiagoefmoraes]

Includes a .livemd file to help with github-linguist/linguist#5672

Some samples didn't work with elixir 1.6+ so I did some yak shaving:

• configured github actions to run in elixir 1.5 to 1.13
• fixed the code for elixir 1.6+

If you evaluate the cells now some will fail because of the elixir version. To get all working change the code on Setup section to:

Mix.install([
  {:exsamples, github: "tiagoefmoraes/exsamples", branch: "livebook"}
])

And evaluate all cells with ea to check the outputs.

[msaraiva]

Hey @tiagoefmoraes. Thanks for the PR!

For context, the reason I kind of abandoned this lib was due to the introduction of the elixir formatter a couple of years ago, which makes the tables look awful. However, I just saw this in Elxiir's CHANGELOG:

  * [mix format] Allow plugins to also format `.ex` and `.exs` files

As far as I understood, that means it would be possible now to use the new plugin API to take over the formatting of the samples do...end block. So I guess we can bring back this project to life :)

I always liked to use this approach in tests but now with Livebook, it might get even more useful ;)

[tiagoefmoraes]

I had to disable formatting on samples do...end blocks,

I had a look if I could implement the formatter, but what I understood is that, right now, it only supports plugins for formating sigils or entire files. https://hexdocs.pm/mix/1.13.2/Mix.Tasks.Format.html#module-plugins

[msaraiva]

it only supports plugins for formating sigils or entire files

Yes! The idea is to format the entire file by calling the built-in formatter first, which is available using format_string!/2, then replacing the samples do...end contents afterwards. This way we keep the default formatting and update only what we need.

[msaraiva]

@tiagoefmoraes I just added the formatter plugin! 😉

I'll add some docs later with instructions on how to set it up and then release a new version.