make webfeed ms-tswp compliant

[akarl10]

there seem to be multiple violations of the spec:

https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-tswp/b308d028-b81d-438b-8d64-546c9797beda
The webfeed is supposed to be version 2.x only if the client sends an accept header containing application/x-msts-radc+xml; radc_schema_version=2.0
Only schema version 2.x allow the folder attributes.

Folder naming:
https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-tswp/58596974-442c-4ed1-8e98-388c02cb631a
the root folder is always "/" and every folder begins with that "/"

Subfolder xml node
https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-tswp/cbe33ab1-4826-48f2-a0d6-e920211bda23
The inclusion of Subfolder is only valid if ResourceCollection points to a displayfolder
Looking at
https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-tswp/b563ae90-b262-4d75-a646-0a0b063022ac
they probably mean that in that case only resources of displayfolders are in the xml response, but there exist some subfolders (that might be requested seperatly, but I did not find how that would be acomplished. Maybe they just defined how the xml should look like but did not implement it.

since in feedparser.js and also on the website there is a dependency on the subfolder element this is not going to work in a compliant webfeed (if a compliant webfeed contains subfolders, that folders will not be in the xml).
To do that you would need to enumerate every possible folder and fill that with the subfolders (probably better called something else) element in feedparser.js

[kimmknight]

Nice work! I'm surprised there's not more.