Previously
```rust
handler.layer(RequestBodyLimitLayer::new(...)).with_state(...)
```
didn't work because we required the same request body all the way
through.
* begin threading the state through
* Pass state to extractors
* make state extractor work
* make sure nesting with different states work
* impl Service for MethodRouter<()>
* Fix some of axum-macro's tests
* Implement more traits for `State`
* Update examples to use `State`
* consistent naming of request body param
* swap type params
* Default the state param to ()
* fix docs references
* Docs and handler state refactoring
* docs clean ups
* more consistent naming
* when does MethodRouter implement Service?
* add missing docs
* use `Router`'s default state type param
* changelog
* don't use default type param for FromRequest and RequestParts
probably safer for library authors so you don't accidentally forget
* fix examples
* minor docs tweaks
* clarify how to convert handlers into services
* group methods in one impl block
* make sure merged `MethodRouter`s can access state
* fix docs link
* test merge with same state type
* Document how to access state from middleware
* Port cookie extractors to use state to extract keys (#1250)
* Updates ECOSYSTEM with a new sample project (#1252)
* Avoid unhelpful compiler suggestion (#1251)
* fix docs typo
* document how library authors should access state
* Add `RequestParts::with_state`
* fix example
* apply suggestions from review
* add relevant changes to axum-extra and axum-core changelogs
* Add `route_service_with_tsr`
* fix trybuild expectations
* make sure `SpaRouter` works with routers that have state
* Change order of type params on FromRequest and RequestParts
* reverse order of `RequestParts::with_state` args to match type params
* Add `FromRef` trait (#1268)
* Add `FromRef` trait
* Remove unnecessary type params
* format
* fix docs link
* format examples
* Avoid unnecessary `MethodRouter`
* apply suggestions from review
Co-authored-by: Dani Pardo <dani.pardo@inmensys.com>
Co-authored-by: Jonas Platte <jplatte+git@posteo.de>
