Add 2.4 version info in __init__.py

Merge pull request PaddlePaddle#1429 from juncaipeng/release/2.3-ch1

[cherry-pick 2.3] update docs for release 2.3 (PaddlePaddle#1428)

Fix SETR export bug

Update README.md

Update release note

Merge branch 'release/v0.8.0' into develop

Add danet voc pretrained

Release v0.7.0

Merge branch 'release/v0.5.0' into develop

Save infer model when saving checkpoint