added pre/post swap render events

[Enerccio]

cause everyone loves more events

technically because I do custom rendering and post render hook was before pointer render, which caused blinking cursor, so I added two more events (pre/post swap) so I can use pre swap for my custom rendering

[Cloudef]

Is post_swap useful for anything?

[Enerccio]

added it for sake of completeness but not to me right now at least

[Enerccio]

thinking about it, it might be useful when rendering was redirected and we want to know when swap happened?