It also add some properties such as `border_width`, `border_color`
and `preferred_alignments`.
It also fix a documentation bug where the `margin_topleft` was called
`margins_topleft`. To conform to the documentation, both are now valid
but one should be removed the next time the API changes.
Fixes#1978
This uses DOC_HIDE magic in the actual test code, except for the
template.lua files which do not have it.
Signed-off-by: Uli Schlachter <psychon@znc.in>