Adds support for folding blocks of code

Some code like imports/require blocks, internal methods/helpers etc can clutter the generated docs making it harder to see what's going on.

Inspired by [Atlassian's version of docco](https://bitbucket.org/doklovic_atlassian/atlassian-docco/wiki/writing-docco-comments) I've added the ability to do this sort of thing:

```javascript
//- Imports
var foo = require("something");

// Some interesting code
var bar = new foo();
```

The generated documentation will contain a marker for the code following the //- Imports comment and all code until the next comment - the code is hidden by default but will be shown if you click on the marker.

It also doesn't show the - or } characters at the beginning of single line comments in the generated docs where they are present.

I'm happy to discuss these changes.