GitLab

* [feat] add CPU support to tutorials in examples

* now works on a machine without cuda
* fixes some minor typos

* [cleanup] factorize tutorials in examples

* collects duplicate code across tutorials in helpers.py

* [fix] getData in tutorials now returns iterable

Adds support for:
* Reused layers (e.g. for weight sharing)
* Lazily-constructed layers
* Single-process control via PipeRPCWrapper
* PipelineStyle.AsyncScheudle, which lays the foundation for asynchronous pipeline work by introducing an event loop for each rank/worker to process either activations or gradients as they arrive

Also added examples for multi-process and PipeRPCWrapper