Window position event and support create position via init parms

Hello, me again :) Here is a clean version of what I sent earlier. Let me know if you want to tweaks something.

One thing that would make this a bit cleaner would be to change the initialization `position_(M_MAX_INT,M_MAX_INT)` to `position_(SDL_WINDOWPOS_UNDEFINED,SDL_WINDOWPOS_UNDEFINED)` then no further check against `M_MAX_INT` would be required. I didn't do this was not sure if that define fits inside a int, so played it safe.

Tested on windows and linux to send the event and create window to the initial position if init params are passed.