Use `properties` (etc.) blocks as automatic sections for the `autoclass` directives.

[apozharski]

For classes with lots of properties (for example the Options class in nosnoc) it would be nice to section the properties for better readability. One approach to doing this would be to treat property blocks as sections (possibly with their own "docstrings" which can be added as section descriptions). This would allow for better matching organization when using the autoclass directive.