Option to download chapters by all groups: -a/--all

[AncientMicrowave]

The idea

Add a -a or --all option to download chapters by all groups that have released them

Why this feature should be added to the app ?

This will make it unnecessary to explicitly specify certain groups in a series of commands, allowing the user to sort through them himself later

[mansuf]

I think that option is already exists, but i forgot to write documentation about it. You can use --group option with value all

# This will download all groups each chapter 
mangadex-dl "insert MangaDex URL" --group all 

Sorry about that, i will add this into documentation in next version release