use json as the request body of `/api/users/activate`
Merge pull request #23 from iTakeshi/activation_via_json

use json as the request body of `/api/users/activate`
implement users#destroy
Merge pull request #26 from iTakeshi/destroy_user

implement users#destroy
update README
Merge branch 'master' into reform-structure

Conflicts:
	doc/class_years.md
	doc/sessions.md
	doc/users.md