Preserve line breaks for example cases in substitution plugin docs

[kchr]

Description

Adds line block markup to example substitutions in the plugin documentation, so that each case is shown on a separate line:

The replacement can be an expression utilising the matched regex, allowing us to create more general rules. Say for example, we want to sort all albums by multiple artists into the directory of the first artist. We can thus capture everything before the first ,, & or and, and use this capture group in the output, discarding the rest of the string.

substitute:
 ^(.*?)(,| &| and).*: \1

This would handle all the below cases in a single rule:

Bob Dylan and The Band -> Bob Dylan
Neil Young & Crazy Horse -> Neil Young
James Yorkston, Nina Persson & The Second Hand Orchestra -> James Yorkston

To Do

• Documentation. (If you've added a new command-line flag, for example, find the appropriate page under docs/ to describe it.)
• Changelog. (Add an entry to docs/changelog.rst to the bottom of one of the lists near the top of the document.)
• Tests. (Very much encouraged but not strictly required.)

[semohr]

Thanks for the fix!

I've just enabled auto-merge. If you update the branch, it should merge into master automatically. Let me know if you run into any issues.