CodeMirror: YAML front matter mode

## YAML front matter mode

--- receipt: Oz-Ware Purchase Invoice date: 2007-08-06 customer: given: Dorothy family: Gale items: - part_no: A4786 descrip: Water Bucket (Filled) price: 1.47 quantity: 4 - part_no: E1628 descrip: High Heeled "Ruby" Slippers size: 8 price: 100.27 quantity: 1 bill-to: &id001 street: | 123 Tornado Alley Suite 16 city: East Centerville state: KS ship-to: *id001 specialDelivery: > Follow the Yellow Brick Road to the Emerald City. Pay no attention to the man behind the curtain. --- 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 formatting**~~ ~~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/.

Defines a mode that parses a YAML frontmatter at the start of a file, switching to a base mode at the end of that. Takes a mode configuration option `base` to configure the base mode, which defaults to `"gfm"`.