add object metadata using the HEADERS setting

#130: Add the object metadata using the existing `HEADERS` setting, eg:

```python
# Set headers based on a regular expression in the file name. For example, this can be
# used to allow Firefox to access webfonts across domains.
'HEADERS': (
    (r'.*\.(ttf|otf|eot|woff|svg)$', {
        # Origins to be allowed to make Cross Origin Requests, space separated.
        'Access-Control-Allow-Origin': '*',
        # Max age for the Origin to hold the preflight results.
        'Access-Control-Max-Age': '360'
    }),
)
```