Simplify weekday lists: Mo,Tu,We => Mo-We
* I chose to use a comma for a two-days range, so Mo,Tu rather than Mo-Tu * This always starts on Monday, i.e. it won't do Fr,Sa,Su,Mo => Fr-Mo. Maybe for the USA it would make more sense to start on a Sunday. Or maybe we want to start from the last day that was set, starting Mo, so the above would lead to Fr-Mo. Shorter, but less readable than Mo,Fr-Su, arguably?