v0.4.1

• Implemented MobileNetV2 (#60)
• Improved vignettes so they use nnf_cross_entropy for numerical stability. (#61)
• Implement the full list of ResNet model family (#66, @cregouby)
• Improved how datasets and models are downloaded by using a large timeout by default
  and downloading to temporary file to avoid hard to debug errors when the files are
  corrupt. (#67)