W02 d01 iterators

[tgaff]

• start by doing a little more forEach work
• then move to .map .reduce .filter
• then carefully frame up our own iterator
• finally build each of the main iterators <-- more work coming on this

Note that this PR is based off of the week 02 PR. It'll be a bit easier to read once I merge that one.

[tgaff]

Exercises C have been moved to another repo. (Good call Nathan)