Adding draft for assignment for 2.a.
arithmetic and mapping
new arithmetic mapping patches
new patches for unit 2
new unit two pd patches
additional folders and patches for unit 2 + support
new pd patches and html files for unit 2
more htmls for unit 2
update pd patches and htmls in unit two
update to unit 2 html
Merge branch 'master' into gh-pages
Updating index pages; adding unit 2.