Show the latest version of the basic-cli docs by default

[Hasnep]

Changes the website build script to show the latest version of the basic-cli docs by default instead of the main branch, and moves the docs for the main branch into a folder called main.

The new layout for the www/build/packages folder is:

packages/
└── basic-cli/
   ├── 0.3.2/
   ├── 0.4.0/
   ├── main/
   ├── index.html
   └── ...

where the basic-cli folder contains a copy of the 0.4.0 folder. The various versions are stored in an array, and the latest version is automatically copied from the first element of the array.

Addresses issue #89 and issue #94 in the basic-cli repo.

[lukewilliamboswell]

So I guess we need to update this for each new release?

[Anton-4]

There's been a bit of mixup, on zulip I was talking about "Should we display the code for the latest release when going to https://github.com/roc-lang/basic-cli instead of the main branch". I think we should keep the docs site https://www.roc-lang.org/packages/basic-cli pointed to the main branch to prevent issues when the URL is shared, for example when someone thinks that they are sharing the docs for 0.4.0 but the content changes over time.

I also set up the www build script yesterday here to auto-detect all docs archives and set up docs sites for all releases that have docs, because that version requires no changes when a release is made I'm going to close this PR in favor of that one. I still appreciate the effort though @Hasnep ❤️