Added foldRight from Listing 3.2
Added length and foldLeft (3.10,3.11)
Rewrote sum, product, and length using foldLeft (3.11)
Reimplemented foldRight in terms of foldLeft
Changed foldLeft to the solution implementation (instead of using a helper function with acc, consider z the acc and recurse on foldLeft). Implemented reverse and append. Append is correct but not good
I realized that my foldRight implementation was incorrect. So I fixed it, which meant reimplementing reverse in terms of foldLeft. Now reverse looks better.