Achievements users
Users which earned an achievement

GET /v2/achievements/:achievement_id/achievements_users
Return all the achievements users of the given Achievement

GET /v2/achievements_users
Return all the achievements users

GET /v2/achievements_users/:id
Get an achievements user

POST /v2/achievements_users
Create an achievements user

PATCH /v2/achievements_users/:id
Update an achievements user

PUT /v2/achievements_users/:id
Update an achievements user

DELETE /v2/achievements_users/:id
Destroy an achievements user