Merge pull request #2 from amrdraz/api

API Documentation
Merge pull request #10 from amrdraz/api

Fixes issue with mixed up User post response/request Body.
Merge remote-tracking branch 'remotes/origin/api'

* remotes/origin/api:
  Changes user_id field to plain old id in api documentation
  Updates empty responses in course resource to have status code 204
  Adds projects_url attribute to course resource
Merge branch 'api' of https://github.com/amrdraz/java-project-runner into api

* 'api' of https://github.com/amrdraz/java-project-runner:
  Adds X-Auth-Token header field to get users collection
  Adds GET /users collection endpoint