init api app
update settings.py : add api to installed_apps
add requirements.txt : add packages for REST framework
update settings.py : add rest_framework to installed_apps
update routes : /api
init README.md for API
error fix : add urls module in api apps
add UserSerializer : return id and email
add UserList API
rename test_user_serializers to test_user_serializer
add TeamSerializer : return id and name
add TeamList API
error fix : rename test_api_test_list to test_api_team_list
add TeamDetail API : look for name
update teams model : set create_time automatically
add TeamUserList API : listing all users belongs to a team
add ProjectList API
add TeamProjectList API : listing all projects belongs to a team
update README.md : /api/users/
update API Usage Guide : basic retrieve