doc: use a more topographical ordering for document sidebar.

Now that the latest LDoc doesn't enforce strict alphabetical
ordering, reorder the documentation into a more topographical
order for easier reading.
* doc/config.ld (file): Reorder for clarity.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
doc: distinguish object and class methods in object doc-comments.

* ext/std/object.lua (clone): Rename first argument to self, and
remove associated @param as a hint to LDoc.
(stringify, totable): Likewise.
(metatable): Document important fields.
(metatable.__call): Add documentation.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>