CMakeLists.txt: use option() for build options to play nice with ccmake and cmake GUIs
CMakeLists.txt: use option() for build options to play nice with ccmake and cmake GUIs

linfengfeiye/badvpn,LazyZhu/badvpn,LazyZhu/badvpn,chrisballinger/badvpn,Git-Host/badvpn,linfengfeiye/badvpn,linfengfeiye/badvpn,PowerOlive/badvpn,tempbottle/badvpn,PowerOlive/badvpn,binondord/badvpn,PowerOlive/badvpn,chrisballinger/badvpn,linfengfeiye/badvpn,linfengfeiye/badvpn,tempbottle/badvpn,tempbottle/badvpn,PowerOlive/badvpn,LazyZhu/badvpn,binondord/badvpn,Git-Host/badvpn,LazyZhu/badvpn,binondord/badvpn,Git-Host/badvpn,binondord/badvpn,tempbottle/badvpn,Git-Host/badvpn,LazyZhu/badvpn,binondord/badvpn,PowerOlive/badvpn,chrisballinger/badvpn,Git-Host/badvpn,chrisballinger/badvpn,tempbottle/badvpn