Make window resizable again.

Note: I can't simple place SDL_WINDOW_RESIZABLE in _fullscreen_modes[] because SDL ignores this flag in SDL_SetWindowFullscreen and if the user started the game in fullscreen and switched to window, it wouldn't be resizable.
The way I did it is the only way I know to make the window resizable regardless of whether the game was first started in window or in fullscreen.
Fixes #249
Merge pull request #252 from adrian17/resizable_fix

Make window resizable again.
Merge pull request #253 from duncanspumpkin/fix_249

Fixes #249
Fixes issue where sound stops working after cancel is pressed
Merge pull request #254 from duncanspumpkin/fix_exit_sound

Fixes issue where sound stops working after cancel is pressed
Fixes #218 @adrian17 did all the work for this fix.
Merge pull request #255 from duncanspumpkin/fix_218

Fixes #218 @adrian17 did all the work for this fix.
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