New API: create file in repo

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Specs for Create file API

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Add docs for create file API

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Merge branch 'feature/api_create_file' of /home/git/repositories/gitlab/gitlabhq