Fix more overload counts in README
Fix more overload counts in README

Applies to:

- ToDelimitedString
- Unfold
- PartialSort
- PartialSortBy
- GroupAdjacent
- Aggregate
- Cartesian
- FallbackIfEmpty

This is a squashed merge of PR #712 that:

- closes #703 (PR)
- closes #704 (PR)
- closes #705 (PR)
- closes #705 (PR)
- closes #706 (PR)
- closes #707 (PR)
- closes #708 (PR)
- closes #709 (PR)

morelinq/MoreLINQ,morelinq/MoreLINQ