config-file for astyle

to enforce a simple CodingStyle
enable GLEW_MX when using internal GLEW with multicontext-support
disable code when building for MULTICONTEXT

when building GEM_MUILTICONTEXT, we want to get rid of GemWinCreate and friends
disable GemWinCreate and [gemwin] in MULTICONTEXT mode
[gemmouse] to be replaced by an abstraction