add impressionist to gemfile
add view_count function
add category_count in topic.index.html
add roo gem
recover pv to impressions_count
two ways to initialize_page_view

way 1:
rake db:initialize_page_view

way 2:
require "#{Rails.root}/lib/page_view.rb"
set_page_view
rename task
a lit fix
Merge pull request #13 from tengcong/zyc

two ways to initialize_page_view