static assets directory copy

[eggcaker]

right now , the o-blog does support the style directory copy to publish dir, what if I have a assets directory which container some blog images or videos, yes , I can put this foder in to templates/style/. but if :

.
├── assets
│   ├── img
│   └── videos
├── blog.org
└── themes
    ├── my-theme
    └── o-blog
        └── style

should be better , then we can extract themes and share.

[renard]

Fix in d05bdc7