Switch Showdown to fork

fixes #2312

- showdown fork understands more html tags
Update README.md
Update CONTRIBUTING.md
Merge pull request #2451 from ErisDS/showdown-fork

Switch Showdown to fork
Removing typography extension

issue #2312

- The typography extension is still interfering in HTML blocks, reference style links and other bits and pieces it probably shouldn't be :(
- We'll add it back when it's ready.
Merge pull request #2452 from ErisDS/typography

Removing typography extension
Properly display escaped tags in editor.

fixes #2149, fixes #2453
- Escape tag before displaying in editor tag widget
Showdown fork now has a version

fixes #2454
Merge pull request #2456 from ErisDS/new-showdown-version

Showdown fork now has a version
Improving the showdown extensions

fixes #2381

- renamed the ghost extensions
- added new html tests
Merge pull request #2384 from ErisDS/showdown-refactor

Improving the showdown extensions
Add XML-RPC ping

closes #2148
- Added core/server/xmlrpc.js
- Hook into post::saved to ping when a published post gets saved
- Added node package to hook into http requests
Merge pull request #2150 from halfdan/2149-tag-display

Properly display escaped tags in tag editor.
Merge pull request #2435 from halfdan/2148-rpc

Add XML-RPC ping
Updating to Casper 0.9.3
Bump version to 0.4.2-rc1
Tag archive body_class

closes #2473
- Show tag-template class on tag pages
- Show tag-{{name}} class on tag pages
- Show archive-template only on second page of tag pages
Adding event preventDefault on toggleFeatured function
Merge pull request #2474 from halfdan/2473-tag-body_class

Tag archive body_class
Merge pull request #2477 from AgtLucas/toggle-featured-post-prevent-default

Adding event preventDefault on toggleFeatured function