Add `maxValueLength`

[Justineo]

Like maxSelectorLength, to split value over multiple lines only if its length exceeds the specified limit.

I got results seemed weird now:

.x {
    transition-duration: 0.5s,
                         2s;
}

The following format seems prettier:

.x {
    transition-duration: 0.5s, 2s;
}

[ben-eb]

Makes sense. The logic for the maxSelectorLength needs a bit of cleaning up, so will do #1 at the same time.

[Justineo]

By the way, I'm using perfectionist to generate formatted code showcase for my Less mixin library est and it works quite nicely now :)

[ben-eb]

Nice! 👍