feat: Import/Export podcasts through opml file

[aarcex3]

An opml is basically a xml file through which one can manage their podcasts subscriptions and move them from one podcast player to another.
E.g, this is what my personal podcast collection looks like.

It would be nice to have the option to import/export my podcasts into/from musicpod.

Other podcasts player have that option:

• Antennapod
• Tsacdop
• Podcast Addcit

[allansrc]

I've found myself looking for it last week.
I'll try to do something to that

[Feichtmeier]

Interesting! This should be some basic feature I heard
On top of that #36 is planned when it is ready
Thanks @allansrc if you take the time, let me know if you need help