Use fenced code metadata to annotate both file location and language

[trek]

From the common mark spec:

The line with the opening code fence may optionally contain some text following the code fence; this is trimmed of leading and trailing spaces and called the info string. The info string may not contain any backtick characters. (The reason for this restriction is that otherwise some inline code would be incorrectly interpreted as the beginning of a fenced code block.)

Where we annotate the code's language

```javascript
var someCode;

We can annotate filename and extension:

```app/templates/foo.hbs
{{rock-on}}

We have a custom highlighter that outputs particular markup/styles for specific languages.

A PR that addresses this Issue will:

• continue to detect bare named language fences
• begin to detect language name from file path fences
• output nice markup/style that decorates an HTML code block something that shows file location

@danmcclain has a sample markup/design

[nicolechung]

Should I update my current PRs to the guide, or wait until this new change has been made?

[trek]

I'd update current PRs and Issue this can be a blocker for merging those

[danmcclain]

@trek Anyone covering the new custom highlighter? If not, I can take a stab at it, seems reasonable. We're going to really need to detect 2 different file types, js and hbs, right? Or are there css and html fences needed too?

[rwjblue]

@danmcclain - Its all yours :)

[danmcclain]

@rwjblue Can you confirm file types in guides? I'll try to get something in place this weekend

[rwjblue]

@danmcclain .hbs, .js, and .html should cover 90% of what we need, but it is possible that we want .css at some point also...

[joostdevries]

And considering the CLI portion, .json might also be a good idea (package.json, bower.json). Apart from files, any way we can illustrate command-lines?

[nicolechung]

For the JS files, is it going to be in this format?

```app/components/my-component.js
// javascript goes here

NVM...just read the commit. Updating now.