InputWritr: a first revamp

[JoshuaKGoldberg]

Cleans up InputWritr a bit by improving some of the docs and function names.

• Adds partial unit test coverage
• Moves alias conversion to UserWrappr, where it belongs
• Renames makePipe to createPipe (I like "create" more for this)_
• Removes a few unused areas of code

Filed #317 to tackle a more complete overhaul of the package long term.