x11: fix --wid=0

Another fallout resulting from the changes whether or not to wait for
mapping the window. In this case, it obviously makes no sense to wait
for mapping, because the root window is always mapped. Mapping will
never happen, and it would wait forever.

Fixes #1139.
CC: @mpv-player/stable
manpage: remove non-existing ratio-pos property

Use percent-pos instead, which is exactly the same, except with the
range 0.0-100.0.

I'm not sure how this got there; it was probably introduced and then
removed again as percent-pos got more precise.

CC: @mpv-player/stable
command: restructure overlay_add code

Somewhat more flexible: now there's a separate overlay struct, and you
don't need to coerce all state into struct sub_bitmap. Also, removing
the previous mapping (munmap call) is now all in one place, the
replace_overlay function.

Makes the next commit easier to implement.
command: allow passing memory addresses to overlay_add

For the sake of libmpv. Might make things much easier for the user,
especially on Windows. On the other hand, it's a bit sketchy that a
command exists that makes the player access arbitrary memory regions.
(But do note that input commands are not meant to be "secure" and never
were - for example, there's the "run" command, which obviously allows
running random shell commands.)
command: don't show message on "osd" command by default

Apparently this was not very popular.

CC: @mpv-player/stable
man: replaced : with , in broken --lua-opts osc example

--lua-opts is a key-value list, so the option parser accepts only commas.

Signed-off-by: wm4 <wm4@nowhere>
CC: @mpv-player/stable