Previously the function signature was inconsistent throughout
src/fe-gtk/plugin-notification.{h,c}: One file had the signature
int(void), while the other had int(void *). Since this type mismatch
might lead to problems (especially with LTO) and the (possibly provided)
function argument isn't used in the function's definition, this commit
sets int(void *) as function signature for both the declaration and
definition of the function.
Fixes: https://github.com/hexchat/hexchat/issues/2726
This setting doesn't work on most platforms
including some notification daemons on linux.
Where it does work I think it is bad behavior
to default overriding their defaults anyway.
It's most valuable use was likely win32
tray balloons which no longer exist.
This splits notifications up into multiple backends
currently only libnotify on unix and win8 toasts.
The win8 backend was originally written by @leeter
though heavily modified.
