Rename generic filenames to something more useful - enhancement

[tonywhitmore]

This is part enhancement, part bug-fix really. Some feeds use a generic filename for the download file, such as media.mp3. One example is the Adam Buxton podcast. The RSS feed is here: https://rss.acast.com/adambuxton

So for example the URL is https://media.acast.com/adambuxton/ep.41-marcmaron/media.mp3 and the file is saved as media.mp3. This is obviously not very useful or helpful to the user, but is probably the "correct" behaviour.

It would be more helpful if the file could be saved with a name like ep.41-marcmaron.mp3 (i.e. extracted from the URL) if possible.

[mlj]

This is partially addressed by commit c337cc0, which will appear in the next major release. See issue #13.