Fixes modal fading inconsistency problem by disabling jQuery's
transition and allowing CSS to do its thing

closes #2400
- Removed fadeIn, jQuery's animation
- Added show(), which only manages display, giving transitions to CSS
Improving the showdown extensions

issue #2381, issue #2312

- renamed the ghost extensions
- added typography to the tests so we can see what is broken
- added new html tests
- commented out typography / removed it from use because it is currently
  too broken
Switch Showdown to fork

fixes #2312

- showdown fork understands more html tags