Make ij.py.show better

As discussed on the Image.sc Forum, we want ij.py.show to do a reasonable thing as conveniently as possible, while also supporting passing in hints for how best to render. Considerations:

1. No extra dependencies. We can use matplotlib or pillow or whatever to do the rendering, but we don't want to require any of those as hard dependencies because not everyone wants to use the show function. It would be nice to have a reasonable series of fallbacks for default behavior that checks whether various supported libraries are available.

2. Ability to pass arguments stating A) which renderer to preferentially use if available, and B) optionally, "hints" parameters for that renderer. We can use kwargs, with each supported viz backend looking for its own key/value argument pairs.

Start by inspecting the existing ij.py.show entry point and the linked Image.sc Forum discussion. Define a renderer preference and hint interface, then evaluate fallback behavior for optional matplotlib, pillow, or other supported libraries. Done means show works without extra hard dependencies and accepts renderer-specific hints.