Merge branch 'stable'
Add links and info back about Elm Reactor
Workshop bolded sentence, mess with indentation, add a link to 0.13 announcement
Trim down intro to be clearer and hook-ier
Try to make the flow better when describing error messages
Switch first to gifs to youtube videos
Switch to video for code swapping example
Add a note about hiding the debug pane
Switch error message example from gif to youtube video
Need better example of a side-effect
Merge branch 'master' into stable