Add example of implementing nil on protocols
Mention we can't extend protocols with other protocols
Add a slide for conflict resolution
Add protocol introspection helpers
Add deftype example and extend/reify stubs
Add record import slide
Clarify reify
Add reify slide
Add clojure internal types implementations
Remove indent of list items

Otherwise markdown doesn't pick them up
Unexistng classes should not break doc
Fix some issues in lecture 11