BasicSR v1.4.0 Release Note

🚀 Long time no see ☄️

This is the first time that BasicSR is released under the XPixelGroup :-)

✨ Highlights
✅ Add training codes of BasicVSR++
✅ Add inference code of BasicVSR++
✅ add psnr ssim pytorch version
✅ add LDL loss
✅ Add online document: basicsr.readthedocs.io/en/latest/
✅ update loss registry
✅ add realesrgan to basicsr
✅ support registry with basicsr suffix

📢📢📢
我们正在准备 BasicSR 的📕中文解读文档。将在近期 release :-)