renamed "close" to "destroy" event to match other output-backends
use "window exposed" for winrefreshCb()

to match SDL
use 'Space' instead of ' '
document messages
properly cleanup context when calling destroyGemWindow()

also delete extroneous contexts when creating new ones
build-system multi-context support

only the code is missing :-)
don't call GLEW-stuff before calling glewInit()