Added missing include needed for stderr.
Removed an superflous call to SDL_Flip instead DrawGame.

The caller of DrawGame does the flipping.
Added missing calls to map RGB values of the green blocks and player
blocks to the apporitate pixel format.

This fixes a problem where the green blocks would sometimes have blue
stripes through it.
Updated stacker to use SDL2.

Most of the internals have stayed the same but the window creation and
managmenet has mainly changed.