SceneGraph: doc++
Platform: deinline default event handlers.

They can't be used as inline anyway.
Platform: added no-op GlutApplication::keyReleaseEvent().

GLUT doesn't have key release events, this function is included only for
compatibility with other toolkits and doesn't get called at all.
Platform: document the intention better.
Platform: added ScreenedApplication class.

Better API for handling more than one application screens (context
switching, event propagation etc.). Taken from Push The Box, updated to
current coding style and templated.
Shaders: minor cleanup.
Shaders: fixed Flat shader.

It is now [0] days since last copypaste error.
doc: documented Plugins directory.