v0.4.0

• Use js.yml & css.yml to control assets.
• Now can build assets via console command python manage.py build_assets.
• Fix bugs & add external paramter & better warning info for urlFor js function.
• Upgrade permission to 0.3.0.
• Upgrade bootstrap to 3.3.4.
• Rm url_prefix when register blueprints.
• Add viewport meta tag to head.
• Add absolute_url_for helper, and inject as jinja2 global.
• Add mkdir_p to helpers.
• Refactor utils.uploadsets.
• Track avatars default image.
• Update color vars in utils.less.