Merge pull request #35 from anniezhn/master

Working more on lessons!
Some more definitions
Merge pull request #36 from anniezhn/azhang

Azhang
moved files
Merge pull request #37 from anniezhn/azhang

moved files
changed
Merge pull request #38 from anniezhn/azhang

changed
more changes!
Merge pull request #39 from anniezhn/azhang

more changes!
Merge remote-tracking branch 'origin/master' into tnichols