searchPath parameter for wiring.appendFiles

This adds support for adding an alternative search path to `wiring.appendFiles` as described in #176(*). Because `searchPath` is now the sixth parameter to the function I thought I would be wise to allow passing an object instead, especially since `attrs` is optional. I chose to not update the shorthands for this, because this is probably a rarely used feature.

(*) where I can't append code to, because github's API is throwing an HTTP 500 at me. :angry: