Make the dump tree output more compact.
Rename tests.
Add initial (buggy) support for lists.

BUG: Nesting doesn't work.
- Now writemime(io, "text/plain", ...) returns a dump tree.
- Update the jdoc program to treat "--plain" as before.
Remove :docstring property from root node (verbose and not used).
Improve AsciiDoc compliance for indentation inside lists.