ri Should Support Searching by Filename

Some libraries like io/console and e.g. the extra methods in date are hard to search for because they don't define their own namespace, and aren't distributed as separate libraries. To assist in finding functionality, ri (and other tools?) should allow the user to search documentation using the file name (which is often the "common name" for the unit of functionality). So, for example:

$ ri io/console   # Maybe a specific switch to force filename lookup?
Located in path/to/io/console

IO
IO#getch
…

The info is already available in the data for the most part (e.g. with ack -u "io/console" $(ri --list-doc-dirs) works for this particular case), just needs to be presentable.

Start at the ri command's search behavior and inspect how the existing documentation data exposes source filenames, using ri --list-doc-dirs and the io/console example as references. Done means a filename such as io/console can be searched and presents its path and documented entries, with the lookup behavior or switch decided consistently.