GitLab

* Doc extensions to some APIs
* FIx the benchmark and tutorial

Adds support for distributing pipeline stages across multiple processes (and therefore multiple machines)
* Adds a style argument to the Pipe constructor, defaulting to PipelineStyle.SingleProcess, but also supporting PipelineStyle.MultiProcess
* Added support for lazy construction of modules (see lazy_construction for an example)
* Added two implementations of inter-process communication: one based on rpc with globally visible queues, one based on send/recv
* Copied all the relevant tests from tests/pipe to tests/pipe_process and modified them to exercise PipelineStyle.MultiProcess

Add a small tutorial, similar to the OSS README

Also updated canonical_url to be fairscale.
Also removed unnecessary htmi_theme_path.

Needed for working correctly with readthedocs.org