add blog model
added model test
changed ways to categorizing
modified post model and add basic blog templat
finished tag & post relation
add fb comment plugin and add dynamic heading
add pagination and canceled turbolink
add PostsController test
improved PostsController's test and added TagsController's test
Merge pull request #6 from st0012/blog

Add basic Blog feature
has tag/category system
can create post/page via post model