* Add README.md

* Update url of images.

* Add images.

* Add usage.md

* Add demo.md

* Fix demo.md

* Add model_zoo.md

* Fix pretrain models download in model zoo.

* Refine documents.
1. Rename python to Python
2. Fix README.md: vgg->VGG, resnet->ResNet, mobilenet->MobileNet
3. Rename flops to FLOPS

* Move docs of PaddleSlim from models.fluid.PaddleSlim to models.PaddleSlim

* 1. Introduce model format in README.md
2. Merge results of combined strategies into one table.

* Refine README.md

* Refine README
1. Fix some terms in README.md
2. Fix description of model format in README.md
3. Add Channel-Wise into feature list
4. Rename 'paddle mobile' to 'Paddle Mobile'
5. Add comments for dynamic quantization and static quantization
6. Add entry url for Model Zoo in README.md

* Refine README.