01_layers: create docments

[warner-benjamin]

Add docments to 01_layers.

See the style guide and contribution guide for more details (links will be added when created).

This requires a moderate to advanced familiarity with both fastai and PyTorch, as the methods cover a wide range of fastai implementations and customizations of PyTorch layers.

Docments progress:

• [ ] Basic manipulations and resize
• [ ] BatchNorm layers
• [ ] Inits
• [ ] Convolutions
• [ ] Embeddings
• [ ] Self attention
• [ ] PixelShuffle
• [ ] Sequential extensions
• [ ] Concat
• [ ] Ready-to-go models
• [ ] Time Distributed Layer
• [ ] Swish and Mish
• [ ] Helper functions for submodules