Dropblock

**Changes:**

- Performance improvements of block mask computation (21)
- Performance improvements of bernoulli mask computation (22)

**Bug Fixes:**

- Fixed bug where too big block sizes lead to wrong block mask size (20)

**Notes:**

- Should be now compatible with PyTorch v1.0

Fixes a minor issue with the DropBlock2D block mask generation.

**Breaking changes:**

- DropBlock is now DropBlock2D
- feat_size argument no longer exists, now dinamically computed

**New Features:**

- DropBlock3D
- LinearScheduler
- ResNet9 on CIFAR10 example script

**Bug Fixes:**

- Refactored forward pass of DropBlock
- FIxed gamma computation
- Fixed CUDA compatibility

Index based DropBlock implementation