add devise_invitable gem.
add devise invitable table for user.
add devise invitation view.
user apply invitations.
invite user.
add invite reason to users.
fixed rspec error.
change invitation form style.
use html-pipeline since dependencies on charlock has been removed

refs #264
user can upgrade to create event.
send invited email.
add directly registrtion feature test.
Merge pull request #264 from ywjno/master

add platforms option with unicorn gem
Merge pull request #265 from doitian/switch-back-to-html-pipeline

use html-pipeline since dependencies on charlock has been removed
add exception notification gem. close #248
merge.
fixed ruby 2.0.0 run zc error.
add pry-nav gem for quick debug.
add ruby-2.0.0 for travis-ci test.
upgrade rails to 3.2.12