fix SEO problem

1. output '/t/123' link in ATOM feed
2. redirect '/topics/123' link to '/t/123'
add constraints to /topics/:id

so we only redirect '/topics/123' paths
add sitemap support
add root url and pages url to sitemap
show meta description tag on homepage
update meta description tag

output meta description tag in node/topic/member page
update canonical path support
update thin to 1.5.0
add missing title/meta description tag
basic homepage in pb2 style
finish homepage
finish node show page
finish "font-end" pages
update page's design
update my following page
update details

1. add custom css
2. fix comment shortcut js
3. fix notifications style
4. fix node link style in safari
update markdown parsing
update preview
show ad
update session & registration form