fix typos
Lecture 4
lecture 04: fix markup
lecture 04: more markup fixes
lecture 04: more fixes
Fix some typos in lecture 4
Updates for questions on lecture
Merge pull request #18 from mdimitrova/04-fix-typos
Add lecture 05
lecture 05: fix typos
lecture 05: content fixes
Merge pull request #19 from tochev/lecture_05_fixes

Lecture 05 fixes
lecture 06: data transformations