Pipelayer

* Adds support for classes that implement the `pipelayer.Step` protocol as steps
* `pipelayer.Step` is now a Protocol
* `pipelater.Pipeline` and `pipelayer.Filter` implement the `pipelayer.Step` protocol
* Updates type hints for pre_/post_process arguments in `pipelayer.Filter` constructor

It's still in beta and bumping the version to 1.0.0 was deferred--despite the breaking changes.

What's New:
* Nested pipelines

BREAKING CHANGES:
* `pipelayer.Pipeline.filters` attribute renamed to `steps`
* Adds support for `pipelayer.Pipeline` instances as steps
* `pipelayer.Pipeline` removes factory method, and implements a constructor that takes `steps` and `name` as args
* `pipelayer.Pipeline.run` and `pipelayer.Filter.run` method signatures updated.
* Removes `pipelayer.Settings` base class
* Removes `settings` and `log` attributes from the `pipelayer.Context` class
* Removes `pipelayer.exception.PipelineException`

* Adds support for static/module/lamba functions as well as `pipelayer.Filter` types as Pipeline Filters
* Adds Basic signature validation for filter functions
* context property in `pipelayer.Filter` is typed as `Union[Context]`
* Handles all exceptions raises by filters and raises a `PipelineException` with the original exception assigned to the `inner_exception` property

* Pipeline composed of single-method classes that inherit from `pipelayer.Filter`