Merge pull request #36 from sowa-snow/fix_empty_data_yml

Fixed that loading user account data is failed when 'db/data.yml' is emp...
Remove the parameter of App::user
Add master config file verification
Merge pull request #37 from sowa-snow/feature/config_validation

Add the master config file verification
Merge pull request #40 from sowa-snow/workings/user

Remove the parameter of App::user
Remove [] operator override of Pathname class
Merge pull request #41 from sowa-snow/workings/filepath

Remove [] operator override of the Pathname class
Refactoring app.rb
Merge pull request #42 from sowa-snow/workings/refactoring/app.rb

Refactoring app.rb
Quit using the misleading function 'Token::start_with?'.

Fix #43.
Now 'Ex.3.1_2' isn't a child of 'Ex.3.1'.
Merge pull request #46 from chiro/issue-43

Quit using the misleading function 'Token::start_with?'.
Add a new type of reports: 'closed'.

Students cannot post 'closed' reports but super users can browse them.
Add an example of closed reports.
Add a new kind of ArgumentError.
Merge pull request #48 from OKU1987/oku/closed

Oku/closed