mingw-w64 fixes and project layout change

This branch provides fixes for mingw-w64 (many thanks to DG) and changes the project layout from neo/ to repository root. libraries are moved from neo/libs to libs and neo/*cmake/premake scripts are moved to scripts. Also the build scripts are refactored into a modular model which should make upgradinging the libraries easier and clarify the source boundary between the engine and the libs also in means of the code license.