Ver 0.2.0

What's New:

• Removed redundant components in ShadowCaster2dBundle.
• Moved redundant Bevy features into dev-dependencies.
• Added alpha_threshold to ShadowMap2dConfig.
• Samples of PCF is no longer limited to 32.
• Added SpotLight2d.
• Added alpha map to clip shadows, which improved shadow accuracy.
• Added catalinzz feature. It will be enabled as default. In the future, in order to support more fancy features, there will be more shading approaches like SDF+RayMarching and Ray Tracing, and you can choose according to your needs.

What's Fixed:

• Sprites without ShadowCaster2d still cast shadows.
• Program panics when there's no 2d light in the scene.