Support uploading images via PUT request

[kylef]

HTTP PUT is a common format which other services support (such as https://transfer.sh). It would be awesome to add support for cross-service compatibility. This is simple to use with standard tools like curl, for example:

$ curl --upload-file ~/Screenshots/2021-06-19_14-18-33.png https://img.vim-cn.com/

The service appears to return a stacktrace in this case:

$ curl --upload-file ~/Screenshots/2021-06-19_14-18-33.png https://img.vim-cn.com/

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/tornado/web.py", line 1569, in _execute
    result = self.prepare()
  File "/usr/lib/python3/dist-packages/tornado/web.py", line 2322, in prepare
    raise HTTPError(self._status_code)
tornado.web.HTTPError: HTTP 404: Not Found

This would work something like:

PUT /file.png HTTP/1.1
Host: img.vim-cn.com
Content-Type: image/png

<the contents of the PNG>