assemble/assemble — pull request #157 by doowb (2013-05-13 04:14:14+00:00)
Title: Adding support for optional collections

Adding support for optional collections.

In the grunt file, collections can be specified in options:

```js
assemble: {
options: {
collections: ['archives', 'posts']
}
}
```

In page yaml headers:

```yaml
---
archives:
- 2013
- May
- 12
---
```

`tags` and `categories` are defaults and will always be included as collections.