CodeMirror: GFM mode

## GFM mode

GitHub Flavored Markdown ======================== Everything from markdown plus GFM features: ## URL autolinking Underscores_are_allowed_between_words. ## Strikethrough text GFM adds syntax to strikethrough text, which is missing from standard Markdown. ~~Mistaken text.~~ ~~**works with other fomatting**~~ ~~spans across lines~~ ## Fenced code blocks (and syntax highlighting) ```javascript for (var i = 0; i < items.length; i++) { console.log(items[i], i); // log them } ``` ## Task Lists - [ ] Incomplete task list item - [x] **Completed** task list item ## A bit of GitHub spice * SHA: be6a8cc1c1ecfe9489fb51e4869af15a13fc2cd2 * User@SHA ref: mojombo@be6a8cc1c1ecfe9489fb51e4869af15a13fc2cd2 * User/Project@SHA: mojombo/god@be6a8cc1c1ecfe9489fb51e4869af15a13fc2cd2 * \#Num: #1 * User/#Num: mojombo#1 * User/Project#Num: mojombo/god#1 See http://github.github.com/github-flavored-markdown/.

Optionally depends on other modes for properly highlighted code blocks.

Parsing/Highlighting Tests: normal, verbose.