add codepen demo code snippets
move boxmodel hack to from lessson 3 to 4 and add clearfix hack as well.
Prepare lesson 5.
Distribution and Reading List
add the codepen.io demos which we went thru on lesson 4.
Add some topics on lesson 5.
Merge branch 'gh-pages' of github.com:ga-students/FEWD_HK_3 into gh-pages