Support non-bitmap image type

Enhancement

• Add support for non-bitmap image type.

Fixed

• Fix accuracy loss when generating mipmap (#7).

Fix issue with FilterMipmapJob in newer version of Unity

Fixed

• Fix Burst complain about two containers maybe aliasing in FilterMipmapJob.
• Use Texture2D.Reinitialize instead of Texture2D.Resize from Unity 2021.1 onward.

Fix a few bugs

Added

• Add CHANGELOG.md.

Changed

• Refactor Burst jobs.

Fixed

• Fix typo in README.md.
• Fix performance issue when importing PNG without alpha channel.
• Fix out of bound access in mipmap generation job.

Initial Release

v0.1.0

Implement AsyncImageLoader