* Move all rust crates (except lib) into crates dir, w/o nesting
* Remove stale path from .gitattributes
* Rename lib.rs files for easier navigation
* Rename mod.rs file for easier navigation
* Fix emscripten-version path
* Fix fixtures dir paths
* Use the default rustfmt settings
* Don't use nightly on CI
The minimal UI of the Playground could benefit from some documentation to make it easier for the newer users to understand what's going on. Also added a link to the new documentation from the local playground.
Closes https://github.com/tree-sitter/tree-sitter/issues/1305
