The thread spawned by `Events` to listen for keyboard inputs had knowlegde of
the exit key to exit on its own when it was pressed. It is however a source of
confusion (#491) because the exit behavior is wired in both the event handler
and the input handling performed by the app. In addition, this is not needed as
the thread will exit anyway when the main thread finishes as it is already the
case for the "tick" thread. Therefore, this commit removes both the option to
configure the exit key in the `Events` handler and the option to temporarily
ignore it.
- merge `Style` and `StyleDiff` together. `Style` now is used to activate or deactivate certain
style rules not to overidden all of them.
- update all impacted widgets, examples and tests.
- Remove deny warnings in lib.rs. This allows easier iteration when developing
new features. The warnings will make the CI fails anyway on the clippy CI
stage.
- Run clippy on all targets (including tests and examples) and all features.
- Fail CI on clippy warnings.
