Change the parameter name to omit_single_disc (vs previously zero_disc_if_single_disc)
Add return of 'fields_set' so that, if triggered by the command line `beets zero`, it will still effect the item.write.
Added tests.
Adds a zero_disc_number_if_single_disc boolean to the zero plugin for writing to files. Adds the logic that, if disctotal is set and there is only one disc in disctotal, that the disc is not set.
This keeps tags cleaner, only using disc on multi-disc albums. The disctotal is not touched, particularly as this is not usually displayed in most clients.
The field is removed only for writing the tags, but the disc number is maintained in the database to avoid breaking anything that may depend on a disc number or avoid possible loops or failed logic.
Add a configuration section that lists all options for each plugin.
List options in alphabetic order.
Mention the default value for each option.
Use same sentences to describe concepts common to different plugins eg 'auto
option, install description
