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

Fix label tools bug (PaddlePaddle#224)

Merge branch 'develop' into release/v0.3.0

Merge pull request PaddlePaddle#78 from LielinJiang/dianbiao_contrib

Add mechanical meter to contrib

Update README.md