Update `get_rawio` function with additional functionality

[zm711]

I noticed our docs were building off the deprecated function so I went to switch just the docs and decided to update the get_rawio a bit more.

The argument was filename_or_dirname, but it only checked file extensions. I extended this to accept either including not currently written files. I also added a new argument: exclusive_rawio if this is set to False it will return all possible rawios organized by the one that reads the most files from the directory. If it is a single file then it returns the full list unsorted.