Changed back WaitEvent() and WaitEventTimeout() to use passed-in variable

Signed-off-by: Jacky Boen <aqiank@gmail.com>
Change back PushEvent() to return int instead of bool

Signed-off-by: Jacky Boen <aqiank@gmail.com>
Added test for PushEvent
Merge branch 'master' of https://github.com/jackyb/go-sdl2
rename 'Test*' to '*' because file hierarchy implies they are tests