Suggestion for extending SIGWINCH

[zxuiji <gb2985@xxxxxxxxx>]

Currently it only indicates a change in window size, I expect the
si_code value is also 0 for this signal. The extension will be for
mouse input and the difference will be indicated by si_code being 1,
to avoid issues with x11 vs wayland vs etc a custom structure should
be pointed to in the si_addr parameter. I think the custom structure
should look something like this:

struct ttymouse
{
    uint button_mask;
    int x, y, wheel;
};