🐛 Can't disable line-numbers in a custom feature

[dandavison]

cc @ulwlu @HaleTom ref #307 #340 (comment)

I feel that this should work, but it does not:

[delta]
    line-numbers = true
    features = no-line-numbers

[delta "no-line-numbers"]
    line-numbers = false

Debugging suggests that it may involve delta refusing to visit the line-numbers entry twice:

[src/options/set.rs:393] &features = [
    "line-numbers",
    "no-line-numbers",
]

Perhaps however it should notice that the second entry was associated with a different value from the first.