External storage support

[Acclorite]

Why you want this feature to be implemented? Please describe.
Currently you can get books from internal storage only.

Describe the feature you'd like to be implemented
Getting books from both internal and external storages (SD).

[DeeChael]

WebDAV support

Because I have too many books and my phone is only 256GB, I dont wanna waste too many space on my phone. I stored all of my books on a cloud service like Dropbox and it supports WebDAV. I wanna import books from WebDAV.
I think the book content can be stored in cache when loaded from the webdav server after it is loaded. Though my book is a lot but the size of every single book is only about 20MB. An option can be added to settings to set the maximum cache size.