added a few options

[amirsher]

thanks for your work, I've been using podget until now and i found you project much better.
I've added a few features that more suiting my use case and maybe other will benefit:

1. I like my podcast all in one folder and without config files getting in the way so I added a line in the .podfox.json to put the config files in a different dir (I put them in ~/.podfox).
2. made change so all podcast are downloaded to the same dir so it easy to find them all in one dir and no need to go from folder to folder.
3. added option to import from a list so no need to run import for each feed. for now it works just if the list doesn't have feeds that was already added, not sure if I know how to fix it.
4. added info on creating systemd service and timer.

I'm not py dev and all changes are pretty dirty but works, you can find them all here: https://github.com/amirsher/podfox