Version 1.0

This feature branch is meant to assemble all commits and change for the first official release of the multiupload field. It should be pulled when all features are considered stable.

### Features

#### UI – @nilshoerrmann

- [ ] basic upload: offer a default upload field for browsers that don't support the File API
- [ ] multiple upload: offer a multiupload option based on the File API
- [ ] drag and drop upload: allow files to be dragged if the browser is capable

For reference: https://developer.mozilla.org/en-US/docs/Using_files_from_web_applications

#### API – @brendo 

- [ ] offer a way to upload using classic POST requests
- [ ] offer a way to accept files using the browser's File API