The capabilities are added automatically by the default principal path
handlers in the `caldav` and `carddav` packages. However, using the
custom handler, they have to be passed in manually.
These being missing before was a violation of the RFC and the cause for
issues when using e.g. DavX5 client. This is now fixed.
There is now only one last PR missing before we can start using the
vanilla upstream go-webdav again. Thanks a lot to Simon for his patience
reviewing my PRs!
The filesystem storage backend now implements the required functions to
act as a basic CalDAV server. Some refactoring was done based on the
go-webdav development: introduce a UserPrincipalBackend, a new function
to serve the user principal URL, and more. See this PR for lots of
details: https://github.com/emersion/go-webdav/pull/62
Also adds a simple facility for debug output.
