Minor changes suggested by Matthew Sorensen
Add two other definitions
mapWithIndex is co-recursive

Apparently I'm much stricter about co-recursion than I thought I was,
so we'll delete both silly recursive implementations.
Merge pull request #1 from matthewSorensen/folds

Incorrect Definition of mapWithIndex 
Merge branch 'master' of github.com:zhanrnl/haskell-sofo
Progress on parser assignment writeup
Whoops added the files now
Added the pdf file instead of the ltx file, whoops