Parameterize shared_steps

[nyarly]

shared_examples both allow for parameters to their definition blocks, as well as accepting blocks when they're included to set up their context. c.f. https://www.relishapp.com/rspec/rspec-core/docs/example-groups/shared-examples#passing-parameters-to-a-shared-example-group

shared_steps are reasonably different, but at least one client project uses the parameterization - to arguable effect. I don't think block-for-context makes sense.

For the moment, I'm refactoring these out where I find them, but if a solid use case could be made, I might see about including the feature.