GRAPHICS: Fix some Doxygen comments that seem wrong.
COMMON: Fix some Doxygen comments that seem wrong.
BACKENDS: Fix some Doxygen comments that seem wrong.
ENGINES: Fix some Doxygen comments that seem wrong.
GUI: Fix some Doxygen comments that seem wrong.
AUDIO: Fix some Doxygen comments that seem wrong.
Merge pull request #495 from somaen/docuFix

Doxygen-fixes