Revamp documentation

[saulecabrera]

The objective of this commit is to:

• Bring the documentation up to date, by removing/correcting the stale pieces
• Introduce a new organzation approach to documentation making it easier to evolve it over time.
• Reduce the text-density of the README

In general this commit strives to add as little new information as possible and primarily re-organizes the existing documentation. The only extra documentation is the JavaScript API support, which was lacking as correctly noted in #749 (comment)

Checklist

• I've updated the relevant CHANGELOG files if necessary. Changes to javy-cli and javy-core do not require updating CHANGELOG files.
• I've updated the relevant crate versions if necessary. Versioning policy for library crates
• I've updated documentation including crate documentation if necessary.

[jeffcharles]

Looks good!

Any reason for the leading docs- on the filenames in the docs directory?

Only change I'd really like to see made is the one to remove the duplicate cargo +stable install cargo-hack --locked, others are all nits.

[saulecabrera]

Any reason for the leading docs- on the filenames in the docs directory?

No strong reason. I wanted to make sure that we can easily move these files around if need be (independent of the directory) allowing us to fully disambiguate them from other markdown files (in case we introduce new ones).

[saulecabrera]

I'm not sure why the jobs seem to be stuck. I'll close and re-open.