Syntax highlighting in annotations


Adds two internal variables `highlighter` and `highlightAuto`.
Configures marked to use highlight.js to parse code blocks inside annotations:
```coffee
marked.setOptions {
    highlight: (code, lang) ->
        if !lang then highlightAuto(code).value
        else
            ext = '.' + lang
            if languages[ext] then lang = languages[ext].name
            highlight(lang, code).value
}
```