Update parsedown, v1.0.1
Add ParsedownExtra, v0.2.2
Cloak Parsedown's autolinking feature so shortcode attributes don't get bunked
Start using ParsedownExtra
Image shortcode does not require alt content
Update readme and bump for release
Merge branch 'fix/0.5.1'

* fix/0.5.1:
  Update readme and bump for release
  Image shortcode does not require alt content
  Start using ParsedownExtra
  Cloak Parsedown's autolinking feature so shortcode attributes don't get bunked
  Add ParsedownExtra, v0.2.2
  Update parsedown, v1.0.1