Update README.md
Add week 2 challenge
Update README.md
Update README.md
week 02: clarification of challenge-constraints
Adding Erin's challenge for Week 3
Fix capitilization and make the link a link
Update README.md
Add Week 4 Challenge
Update language in Bonus #1
fixing README

Fixing typo: reduce from from right can be implemented fold from left.
Update README.md

Ugh, an additional typo. Thanks mikew
moby dick - handling duplicate words

@mwynholds - updated examples (pairs and freq) to demonstrate desired behavior when running into duplicate words in the same sentence. I came across this scenario while working through the moby.txt and realize that I never provided any specification; I'm just inventing something. If you've already got a working solution (within some other constraint) - feel free to propose something else.
updates to reflect Aug 11 convo @ C5 SF
BST nodes should be k/v pairs