swirlify 0.5.0

• Removed lp().
• Deprecated testit(). testit() will be removed in swirlify 0.6.
• Added demo_lesson() which replaces testit().
• Added google_form_decode() to help course authors evaluate their students'
  progress in a swirl couse.
• Added swirlify() which starts a Shiny app for authoring swirl lessons.