CodeMirror: GFM mode

GitHub Flavored Markdown

========================

Everything from markdown plus GFM features:

## URL autolinking

Underscores_are_allowed_between_words.

## 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/.