Fixed Project 2: now runs example programs including a0a1a2adone. Also added interrupt for invalid op codes
updated readme with distinction b/t projects 2 and 3
Merge pull request #2 from johnpaulwelsh/gh-pages

Merge pull request #1 from johnpaulwelsh/master
Merge pull request #3 from johnpaulwelsh/master

Pull from master into gh-pages for reposting Project 2