randym/axlsx — pull request #195 by noniq (2013-06-12 21:21:38+00:00)
Title: Allow overriding the 'created' timestamp in the docprops.

Can be specified as option to Package#new:
```ruby
Axlsx::Package.new :created_at => time
```

If omitted, the current time at the moment the document is serialized will be used. This change is therefore fully backward compatible.