add Flask-Restful requirement
rewrite upload code with Flask-Restful
add swagger api documentation
add and document skeleton for DELETE und PUT api
use abstractmethod decorator
red: add (failing) tests for DELETE and PUT api
implement delete in FileSystemStorage
implement delete in DatastoreStorage
implement DELETE rest api
green: implement DELETE and PUT API
refactor: put shared puload code into its own function
formatting
add link to appi documentation to readme
Merge branch 'restful'

fixes #7