Add Upload construct

[t-richard]

See the docs for explanations.

• [ ] More tests
• [ ] Document what is done with CORS ?
• [ ] Axios example ?
• [ ] in depth explanation of wha the function does ?
• [ ] example code for backend processing ?

[t-richard]

See some working examples here https://github.com/t-richard/lift-upload-example

Steps to deploy it are in the README

[tschoffelen]

This is really cool!