Add a new `bevy_text` feature for more granular control over
`Text`-related lenses, and change the `TextColorLens` to require that
new feature instead of `bevy_ui`, as texts _can_ be used without the
Bevy UI crate.

Fixes #68

Add two new methods to the `Tweenable<T>` trait:
- `set_elapsed(Duration)` sets the elapsed time of the tweenable. This
  is equivalent to `set_progress(duration().mul_f32(progress))`, with
  the added benefit of avoiding floating-point conversions and potential
  rounding errors resulting from it. `set_progress()` is now largely
  implemented in terms of and as a convenience wrapper to calling
  `set_elapsed()`.
- `elapsed()` which queries the elapsed time of the tweenable. This is
  equivalent to `duration().mul_f32(progress())`, again with better
  precision.

The elapsed API is the recommended way going forward to manipulate a
tweenable's time outside of the normal `tick()` flow. It supersedes the
progress API.

This change purposedly skips any discussion about what happens to
completion events when `set_progress()` or now `set_elpased()` is called
with a lower value than the current one to seek time back. This design
issue is logged as #60 and is still pending. The change also partially
addresses #31, but without removing any existing API or feature.

Fix the animator speed applying, which got broken as part of the
refactor of #44.

Add a `speed()` getter to both `Animator<T>` and `AssetAnimator<T>`.

Add some simple test for speed, but this is not enough to make sure the
feature doesn't regress, so logged #62 to follow-up with a proper
regression test.

Fixes #61

Fix the repeat mode being broken after the first iteration due to
`AnimClock::progress()` reporting a progress greater than `1.`, which was
breaking the logic of `Tween` and `Lens`.

Also fix `Tween::rewind()` not restoring the original tween direction when
using a repeat strategy of `RepeatStrategy::MirroredRepeat`.

Fixes #42

Make `Delay::new()` panic if a zero duration is passed as argument. Fix
the `menu` example to skip inserting a `Sequence<Transform>` containing
a zero-duration `Delay`.

Bug: #41

This reverts commit 87ac60b2.

Upgrade to the latest released version 0.8.0 of Bevy.

Add a new `bevy_asset` feature to enable animation of Bevy assets
(types implementing the `Asset` trait). Bevy 0.8 does not contain
`bevy_asset` in its defaul features, so this new feature reflects that
new possibility to build Bevy and í½ƒ Bevy Tweening without support
for the `bevy_asset` crate. The new feature is enabled by default for
discoverability and to prevent a behavior breaking change.

This reverts commit 6a871576.

Remove `TweeningType` and split its functionalities between a new `RepeatCount`
controlling the number of repeats of an animation on one hand, and
`RepeatStrategy` controlling the way an animation restarts after a loop ended
on the other hand. This allows more granular control on the type of playback.

Remove the `tweening_type` parameter from `Tween<T>::new()` and replace it with
builder methods `with_repeat_count()` and `with_repeat_strategy()`.

Remove `is_looping()` from all tweenables, which was not implemented for most
of them anyway.

Fix double-boxing by removing the `IntoBoxDynTweenable` trait and the impl of
`Tweenable<T>` for `Box<dyn Tweenable>`, and instead using some `From`
conversion implemented per concrete type.

This lets you not have to run after every single system and instead just pass in the label.

It needs to be built-in because otherwise you have to completely recreate the animation to change the speed.

Allow a `Tween` to play backward by setting its direction with
`Tween::set_direction()`.

Enable minimal dependencies with new features `bevu_sprite` and
`bevy_ui`, removing the `bevy/render` mandatory dependency. Those new
features are enabled by default, and enable the built-in lenses for the
related Bevy crates. The core `bevy_tweening` crate itself does not take
any optional Bevy dependency anymore, allowing for a slim build with
only the core Bevy functionalities.

Fix some bug lerp'ing colored lenses (`TextColorLens`,
`SpriteColorLens`, `ColorMaterialColorLens`) where the alpha value would
be too high. This only affects non-opaque colors, in that for opaque
blending the resulting alpha was `3.0` which was interpreted as opaque.

- Add `TweenCompleted::user_data` to help identify the tween which
  raised the event.
- Improved several docs.
- Update CHANGELOG.
- Update README with mention of events and callbacks.

Add some new methods and refactor some existing ones to clarify the
playback state of a tweenable, and give increased control to the
`Animator` or `AssetAnimator` to rewind a tweenable, set its progress to
an arbitrary value, or query its current state.

Add a `Tweenable<T>` trait describing a generic animatable tween-like
element.

Expose the three types of tweenables and implement `Tweenable<T>` for
them:
- `Tween<T>`, a single animation
- `Sequence<T>`, a sequence of consecutive animations
- `Tracks<T>`, a batch of animations running in parallel

Clean-up animators to hold a single top-level `Tweenable<T>` and let the
user build any kind of animation hierarchy for themselves.

Allow querying the active tween of a sequence. Use this to improve the
`sequence` example with some text showing the current active tween and
its progress.

Implement some callbacks invoked when a tween anim starts or ends.

Export publicly the asset and component system to allow an app to
manually add them.

- Add `Sequence<T>` for chained tweens
- Add `Tracks<T>` for tracks of sequences running in parallel
- Move most animation-related properties to the new `Tweens<T>` struct
- Add `sequence` example

Import `bevy_tweening` from its old repository.

URL:
https://github.com/djeedai/bevy_extra/tree/main/crates/bevy_tweening

Commit: 1e13a72