Fix Python sdist, update docs, add lint to CI

[texodus]

• Fixed Python .whl support for the pre-build PerspectiveWidget based on feedback from v3.0.0-rc.1. We've found two breaks here, both stemming from the disparity between JavaScript's v3.0.0-rc.1 and Python's insistence on stripping this to 3.0.0rc1. (1) PerspectiveWidget using Python importlib to generate the npm model version, and (2) repack_wheel using the package.json version to generate the wheel's data directory name.
• Add sdist packaging to CI.
• Add lint step to CI and remove clang-format (and may I say, good riddance).
• First-pass update to docs, mostly with an eye towards removing deprecated/removed/etc functionality and syntax. Also removes the API docs section entirely, which will be replaced by docs.rs
• Fixes the link to the build.yaml embedded in the repo's README.md author line CI badge, see this extensive internal discussion or better yet just take my word for it.