Slide corrections & 1 content update

Class2: 
(1) Corrected inconsistent font-family name for "Enotypo" -> "Entypo"
(2) Corrected syntax of linear & radial gradient examples

Class3: 
(3) Corrected itemprop "tag" (no html element was present in example) 
(4) Updated Canvas example with a link to codepen.io example showing html/css/javascript of animation